Mitsubishi Noise Guide
Mitsubishi Air Conditioner Making Noise
When a Mitsubishi air conditioner making noise breaks the usual hush of a bedroom or lounge, it is natural to worry. Some sounds are simply the system doing its job, especially in winter. Others are early warnings from a fan, a motor or a loose part. Here we help you tell the difference on Mitsubishi Electric units, flag the points where Mitsubishi Heavy Industries models differ, and explain when to switch off.
Getting Started
What Details Help You Diagnose a Noisy Mitsubishi?
A noise is much easier to solve when you can describe it well. Before reaching for any panel, take a moment to gather a few facts. They often point straight at the cause.
- Which unit makes it, indoor or outdoor, or somewhere in between?
- When does it happen: at start up, while running, at shutdown or at random?
- Which mode is active, Heat, Cool, Dry or Fan?
- Does it change with fan speed or vane movement?
- Has a code or blinking lamp appeared at the same time?
- Is it new, or has an old sound become louder?
A short phone video with sound is gold for a technician. Intermittent rattles in particular tend to go silent the moment someone arrives to listen.
It also helps to listen from a few positions. Stand directly in front of the indoor unit, then move to the side and finally into the next room. A noise that seems loudest through a wall may be a pipe vibrating inside the cavity rather than the unit itself. Outside, walk around the outdoor unit at a safe distance and notice whether the sound comes from the top, where the fan sits, or lower down near the compressor.
Finally, think about recent changes. New sounds often follow storms, building work, a relocation of the unit or even a fresh round of gardening. Mulch thrown against the outdoor casing, a hose left resting on the pipe cover or a tradesperson bumping the bracket can all introduce a rattle that was not there last week.
Know Your Unit
Does It Matter Whether It Is Mitsubishi Electric or MHI?
For noise, the basic mechanics are much the same. Both makers use inverter compressors, cross flow indoor fans and propeller outdoor fans. Even so, the badge matters when a code appears alongside the noise, because the two brands use different code lists.
Mitsubishi Electric wall splits usually carry MSZ model numbers, such as the MSZ-AP and the flat fronted MSZ-EF. MHI wall splits usually carry SRK numbers. Check the front badge and the side label before you look anything up.
Mitsubishi Electric
Fan motor and outdoor fan faults may be reported with two character check codes. Indoor and outdoor communication faults use E codes.
Mitsubishi Heavy Industries
Faults show as E followed by a number on wired controllers. Compressor protection such as E36 can follow laboured outdoor noises.
Normal Operation
Which Mitsubishi Sounds Are Nothing to Worry About?
A healthy reverse cycle system is never perfectly silent. These sounds are expected and usually harmless.
Light ticking
Plastic panels expand when warm and shrink when cool. Small ticks at start up and shutdown are normal.
Faint hiss
Refrigerant passing through the expansion valve can hiss softly, especially as the compressor changes speed.
Defrost whoosh
In heating, the system reverses briefly to melt frost. A loud sigh and steam from outside are part of the process.
Changing hum
The inverter compressor ramps up and down. A stronger hum at start up that settles later is normal.
Vane motor buzz
The horizontal vanes move on a small motor. A brief buzz as they open or swing is expected.
Drain gurgle
Water running through the drain hose, or wind blowing back up it, can make a bubbling sound now and then.
If any of these grows louder, more frequent or changes in pitch, though, it may be signalling a developing fault.
Possible Causes
Why Is My Mitsubishi Making a Strange Noise?
Below, causes move from the easiest to the most serious. Simple issues are surprisingly common, so start with the left column.
Easy fixes
- Filter not slotted fully into its guides, so it buzzes
- Front panel left unlatched after cleaning
- Dust clogged filters forcing the fan to strain
- Leaves or twigs caught in the outdoor fan guard
- Garden items leaning on the outdoor casing
- High fan or powerful mode selected without realising
Professional repair
- Indoor fan motor bearings wearing and squealing
- Indoor cross flow fan cracked or caked with grime
- Outdoor fan blade chipped, bent or striking its shroud
- Worn compressor isolation mounts transmitting vibration
- Copper pipes touching the casing or each other
- Low refrigerant causing ongoing bubbling or hiss
- Reversing valve buzzing or failing to switch cleanly
- Relay, contactor or board component buzzing
On flat panel models, it is worth knowing how the front opens. Forcing it from the wrong edge can crack clips, and a broken clip can leave the panel loose enough to rattle.
Sound by Sound
What Does Each Mitsubishi Noise Usually Mean?
Use these descriptions as a starting point rather than a verdict. Similar sounds can come from different parts depending on the model and installation.
Rattling or vibrating
Loose panels, screws or debris are common. On the outdoor unit, consider loose mounting brackets or worn rubber feet.
Squealing or whining
Commonly a fan motor bearing. The pitch may climb as fan speed increases.
Grinding or scraping
Something is rubbing. That may be a fan touching its housing or a bearing breaking down. Switch off promptly.
Clunk or bang at start up
Can suggest compressor strain or loose internal parts. This needs prompt professional attention.
Loud electrical buzz
May indicate a failing relay or board component. If there is a hot smell, turn the unit off at the breaker.
Continuous hissing
A loud, steady hiss, especially with poor performance, may point to a refrigerant issue.
Whistling
Air forcing through a clogged filter or gap. In ducted systems it may come from a partly closed grille or damper.
Rapid clicking without starting
A relay or protection device trying and failing to engage. Often electrical, so leave it for a technician.
Owner Checks
How Can You Safely Check a Noisy Mitsubishi?
These checks need no tools and keep your hands well away from fans and wiring. Do not remove screwed covers or reach into the outdoor fan.
Note how the sound stops
Turn the unit off. A noise that stops instantly is often fan related. One that fades slowly may be pipes or panels settling.Refit filters and panel
Open the front panel following the manual, slide the filters fully home, then close the panel until both sides latch.Clean the filters
Vacuum or rinse the main filters and let them dry. Follow the manual for secondary filters, which may need dry cleaning only.Look over the outdoor unit
Switch off at the outdoor isolator first. Then remove leaves and sticks you can reach without putting fingers through the guard.Clear the surrounds
Move bins, plants and hoses away from the casing and the pipe cover.Reset and listen again
Turn off the breaker for a few minutes, restore power, then run at a medium fan speed and listen closely.
Skip the checks entirely if you hear grinding or banging, or smell burning. Turn the unit off at the breaker and arrange a technician.
Codes and Noise
Which Mitsubishi Error Codes Come With Noise?
A noisy motor often trips protection eventually. Our Mitsubishi error codes hub explains both brands’ code systems and how to read them. These pages cover codes that can appear with mechanical or running noises.
U2, high discharge temperature
A Mitsubishi Electric compressor running hot may sound laboured first. See Mitsubishi U2.
E36, compressor overheat (MHI)
On MHI units, a strained compressor can trip on discharge temperature. Read Mitsubishi E36.
E57, refrigerant shortage (MHI)
Low charge can bring hissing or bubbling sounds. Learn more on Mitsubishi E57.
P6, freeze or overheat protection
A fan struggling against a blocked filter can lead to coil protection on Mitsubishi Electric. See Mitsubishi P6.
P5, drain overflow
Gurgling or a humming pump on a cassette may come before P5. Read Mitsubishi P5.
U4, outdoor thermistor
A sensor fault can make the outdoor fan or compressor behave oddly. See Mitsubishi U4.
Climate Effects
How Does Australian Weather Change the Sounds a Mitsubishi Makes?
Local conditions shape which noises crop up. Along the coast in Sydney, Perth and Melbourne’s bayside, salt air corrodes fasteners, brackets and fan hubs. Gradually, parts loosen and rattles begin.
In Adelaide and inland Perth, fine dust is the bigger enemy. It coats indoor fan blades, unbalancing them, and makes motors work harder. Consequently, bearings wear early and start to whine.
Brisbane brings humidity and summer storms. Mould on indoor fans and debris blown into outdoor units are both common sources of new noise. Meanwhile, frosty mornings in Melbourne and Adelaide trigger loud defrost cycles that are entirely normal but often reported as faults.
Ash from bushfire seasons can also coat outdoor coils. While it rarely makes noise on its own, it adds load to the fan and compressor.
Technician Visit
What Does a Technician Check on a Noisy Mitsubishi?
The technician recreates the sound, finds exactly where it comes from and tests the responsible part. A methodical approach avoids replacing parts that were never faulty.
- Run the system in each mode through start, steady running and stop.
- Inspect panels, clips, screws and brackets for looseness or cracks.
- With power isolated, turn fans by hand to feel for rough bearings.
- Check the indoor cross flow fan for dirt build up, cracks and balance.
- Inspect outdoor fan blades and the motor mount.
- Check compressor mounts and isolation rubbers.
- Look for pipes rubbing on the casing or each other.
- Measure motor current and test drive circuits.
- Check refrigerant pressures if hissing or bubbling persists.
Fan motors and fan barrels can usually be replaced without opening the refrigerant circuit. Valve or compressor repairs, however, need an ARCtick licensed technician. Every technician we send holds the licences their work requires.
Keep or Stop
Is It Safe to Run a Mitsubishi That Is Making Noise?
A small rattle from a panel or a whistle from a dirty filter is unlikely to harm the system. Fix the simple cause and keep using it.
Some sounds, however, mean every extra hour adds damage. A grinding bearing can seize the motor. A fan blade that rubs can break apart. A compressor that bangs may be close to a costly failure.
Generally okay
Ticks, a soft hiss, normal defrost sounds, or a rattle that stops once the panel is reseated.
Switch off and book
Grinding, banging, worsening squeals, buzzing with a hot smell, or any noise followed by a code.
Ducted Systems
Why Is a Mitsubishi Ducted System Noisy in the Ceiling?
Ducted Mitsubishi systems sit out of sight in the roof, so their sounds can be confusing. Noise often travels through ducts and seems to come from a grille in another room entirely.
Air rushing at grilles
Closing most zones pushes all the air through a few outlets, which raises air speed and noise. Opening an extra zone usually eases it.
Low drone overhead
An unbalanced indoor fan, or an indoor unit resting on joists without proper isolation, can send vibration through the ceiling.
Rustling ducts
Flexible ductwork can flutter as airflow changes. Loose straps or ducts touching timber frames also creak as temperatures shift.
Repeated clicking
Zone damper motors click briefly when moving. Constant clicking or grinding may point to a damper motor wearing out.
Always check the return air filter first. A clogged return grille makes the fan strain and increases almost every ducted noise.
Night Noise
Why Does My Mitsubishi Seem Louder at Night?
Many owners notice noises only at bedtime. Partly, that is because the house is quiet and traffic has died down. Sound from an outdoor unit also travels further on still, cool nights.
There is a mechanical side as well. In winter, overnight frost brings on more defrost cycles, each with its own whoosh. In summer, the compressor may ramp up as the evening stays warm. Neither is a fault on its own.
However, if the outdoor unit sits on a hard surface near a bedroom wall, vibration can carry into the house. Worn rubber feet or a loose bracket make this worse. A technician can check the mounting and suggest better isolation if needed.
Good to Know
How Do You Keep a Mitsubishi Quiet for Years?
Routine care heads off most noise complaints.
Open more detail
Clean filters every few weeks during heavy use. Dust drives most fan noise.
Keep a clear space around the outdoor unit and trim plants that drop leaves into it.
Ask for the indoor fan to be cleaned during a professional service. Grime on the blades is hard to reach without partly dismantling the unit.
On coastal properties, have brackets and fixings checked for corrosion each year.
Mitsubishi Electric outlines servicing expectations in its warranty terms, so keep service records handy.
If the noise comes with the unit cutting out, read our article on an air conditioner that keeps turning off. If the outdoor unit goes silent, see outdoor unit not running. For indoor fan problems, see AC fan not working.
Book a Visit
How Do You Book a Mitsubishi Noise Check?
We are a booking and dispatch service, not a Mitsubishi dealer or manufacturer. We arrange licensed technicians who work on Mitsubishi Electric and MHI systems across major cities.
Describe the noise, when it happens and where it comes from, and share a recording if you can. See the Mitsubishi air conditioning page for the range we book work on, explore the AC troubleshooting library, or view our locations.
Learn more about our air conditioning service Australia network, or send an enquiry through the contact page.
Questions
Frequently Asked Questions
Why does my Mitsubishi make a whooshing sound in winter?
That is the defrost cycle. Valves switch to send heat to the outdoor coil, melting frost, then switch back to heating.
Is a ticking Mitsubishi faulty?
Usually not. Plastic parts expand and contract with temperature, which causes light ticking at start and stop.
Why has my indoor unit started squealing?
A worn fan motor bearing is the usual reason. It tends to get worse, so book a check early.
Can a dirty filter make my Mitsubishi noisy?
Yes. A blocked filter forces the fan to work harder and can cause whistling. Cleaning it often quietens things down.
Why does the outdoor unit vibrate more than before?
Worn rubber feet, loose brackets or a damaged fan blade are typical causes. A technician can inspect the mounting.
Does a hissing sound mean a gas leak?
A soft hiss is normal refrigerant flow. A loud, steady hiss with weaker performance should be checked by a technician.
Will quiet mode fix the noise?
Quiet mode reduces fan speed and normal running sound. It will not cure a worn bearing or loose part.
Mitsubishi Still Noisy?
If your Mitsubishi is still rattling, squealing or grinding after the safe checks, call us. We will book a licensed technician to track down the sound.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles