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Anyone had their air conditioning make a weird faint whistling/buzzing noise? Turn the ac off it goes away. Very strange... My forum search was unsuccessful.
 

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Sounds like the AC / in car air blower fan (not the AC pusher fan in front of engine bay) could be on the way out - mine is tired in my car (130k miles) and I have a new Hella one to go in. Does the noise change if you adjust the speed using the AC fan control?

Simon
 

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Anyone had their air conditioning make a weird faint whistling/buzzing noise? Turn the ac off it goes away. Very strange... My forum search was unsuccessful.
YES! Finally I think someone else with the same thing I hear. I searched for this a few years back, never found anything exactly like it though on here. I thought it was diff whine when I first bought the car.

I've found that these things will create or stop it:

Switching A/C on or off, also switching A/C from recirculate to incoming air will stop it.
It only starts on mine when I go above 80mph with the A/C in recirc, if I turn off the recirc and/or drop below 80 it will stop.
I think also TILTING the sun roof open will stop it too. Opening it fully probably stops it but too much wind noise to hear it.
 

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Sounds like the AC / in car air blower fan (not the AC pusher fan in front of engine bay) could be on the way out - mine is tired in my car (130k miles) and I have a new Hella one to go in. Does the noise change if you adjust the speed using the AC fan control?

Simon
I don't think it's the blower fan in my case as with the blower on in heat mode or non recirc' mode the noise goes away.

I've noticed when switching the A/C on from just regular incoming "cool" air the volume of air through the vents is lower as it directs air through the evaporator, regardless of in recirc' mode or not. So I think it has something to do with the air duct plumbing, and maybe the exhaust vents on the car?
 

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That's interesting - so it does sound like you have air escaping where it shouldn't under certain circumstances - the ducting under the centre console and front seats seems like a likely place it could be disturbed. The info in this doc may help you isolate which bits do what in the different modes - second time i've posted this in 2 days... things must be warming up!

Simon
 

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Thanks for posting Curtis, I'll read thru' that.

It really sounds like a drone/or rear diff whine or bad rear wheel bearing on some cars, but very faint. Kinda sounds like it's coming from the roof of the car or upper cabin area. Like some kind of air pressure build up causing some rubber seal to give to relieve the pressure? I've not had every nook and cranny apart on these cars yet, but know Honda's have little rubber flaps hidden around the body to relieve air pressure. So I'm wondering if it's something like that? Or some failed seal rubber up front letting too much in coming air at high speeds and some rubber seal is giving way to let the excess pressure out? Hasn't been much of a priority to figure it out lately, I've just been switching the recirc' off if it has bothered me when it happens.
 

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Solidarity. I've had that same noise. It comes and goes with the fan. It sounds like an electronic whirring, but if I shut down the fan it sounds more like a squeaky hamster wheel as it slows down. I just assumed it was the blower fan on its way out, but I'm not brave enough to open up the dash...
 

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Hi - reading through the tech info I posted earlier there is a section on speed dependent flap positions in the AC control - also there is a tiny fan behind the AC control panel itself used for sampling the cabin air, these get gunged up and squeaky over time and worth a check. Not sure it's the issue mentioned here but worth a look if your hunting for the noise. I think someone on M5board did a DIY on this if you search.

Simon
 

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Discussion Starter #9
Yes, this issue is definitely coming from the AC. It comes on randomly at slower fan speeds and immediately stops when the ac is turned off. It will come and go randomly even with the ac switched on. It's a weird faint high pitched buzzing. You will know what I'm talking about if you have it. It sounds like something in the vent causing the noise as air blows past it. The flap idea that was mentioned would seem logical.

I can't find the DIY Curtissp321 referenced but sounds plausible.
 

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My blower fan bearings are noisy on colder days until the car warms up.

Do a test - does the noise change or stop when you go around a corner? That's a characteristic of dry blower bearings.
 

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Discussion Starter #11
No it is strictly controlled by turning the ac on and only at slower fan speeds.
 

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Hi - this is the DIY I found showing the sampling fan behind the AC control panel - don't think this is your issue as you said it was speed dependent - useful link tho:

Link

Simon
 

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Discussion Starter #13
I still have this issue and yes the pitch of the noise that is associated with the air conditioner DOES change as I accelerate and decelerate... Thoughts?
 

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YES! Finally I think someone else with the same thing I hear. I searched for this a few years back, never found anything exactly like it though on here. I thought it was diff whine when I first bought the car.

I've found that these things will create or stop it:

Switching A/C on or off, also switching A/C from recirculate to incoming air will stop it.
It only starts on mine when I go above 80mph with the A/C in recirc, if I turn off the recirc and/or drop below 80 it will stop.
I think also TILTING the sun roof open will stop it too. Opening it fully probably stops it but too much wind noise to hear it.
My M5 has the same issue. It's definitely a whistle and not a buzzing sound. Mine will start as low as 45 MPH with the recirc button on. If you tilt the sunroof it gets MUCH louder. :-/
 

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Hmmm odd. So if you open the sunroof while driving along it gets worse. That means reduced air pressure in the cabin I assume, perhaps pulling more air through the vents.

Long shot, but worth checking your ac 'snorkels' that connect from the firewall in the engine bay to the cabin filter enclosures are connected properly, additional air could be being pulled in through a gap there making a noise. It's easy to damage the clips holding these on over time.

Otherwise my money is still on your main blower fan - managed to remove dash and change mine in 2.5 hours last time - a big job but strangely satisfying... it does look like your car has exploded though about 2 hours in! :)

Simon
 

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Hmmm odd. So if you open the sunroof while driving along it gets worse. That means reduced air pressure in the cabin I assume, perhaps pulling more air through the vents.

Long shot, but worth checking your ac 'snorkels' that connect from the firewall in the engine bay to the cabin filter enclosures are connected properly, additional air could be being pulled in through a gap there making a noise. It's easy to damage the clips holding these on over time.

Otherwise my money is still on your main blower fan - managed to remove dash and change mine in 2.5 hours last time - a big job but strangely satisfying... it does look like your car has exploded though about 2 hours in! :)

Simon
Thanks for the tip. I'll definitely check the "snorkels". Hopefully the dash doesn't have to come apart. If that's the case I'll not use recirc unless absolutely possible.
 
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