Strange sound in my 1992. E34

[baksa]

Hi.

I receantly bought BMW 520i 24v 1992.
It's realy a nice car and I didn't have to spend a lot of money on repairs and stuff, but I'm annoyed with just one thing.
When A/C is on, and car is in neutral (it's a manual shift), strange ans strong sound shakes me every now and then.
It's like someon's blowing into trumpet, strong resonant sound that starts quietly at first, then amplifies and after 7-8 seconds it quiets again and then stops. It seems to me that sound is coming from the speakers, but I'm not sure, because I have 6 speakers installed and looks like the sound is coming from everywhere.
I repeat that this is happening only when A/C is on and it stops when I rev it in place or the car is on the move with gas pedal pressed.
Anyone knows what could be the reason for this strange sound.

[nyc525iTe34]

Does the sound stop when you turn the fan/ac OFF? If so, you might want to look at a few places where the problem might be originating from. Try looking at the following: a loose belt, failing ac compressor, issues with your water pump. Also, some BMW's built in the 90s have problems with the hand break. The noise could also be a coolant related problem - perhaps bleeding the coolant might help.

A very useful book to purchase is a Bentley book for your specific car. It offers troubleshooting solutions and details almost every part of your car.

Hope that helps!

[EonPeon]

What happens if you turn the volume down on your stereo - do you still hear the noise?

Do you have a telephone hands-free set installed? What if you turn that off?

When you turn the A/C on, at what speed is the fan?

What happens if you turn the fan speed down?

It could be you have a tear in the microfilter of the A/C which is causing the resonance...

[EonPeon]

How to replace the microfilter (IF that's the problem..)

http://www.bmwe34.net/e34main/trouble/steeringplay.htm

[EonPeon]

Oops.... wrong URL

It's http://www.bmwe34.net/e34main/trouble/steeringplay.htm

[LMUNick]

Ooops again...its actually this one: http://www.bmwe34.net/e34main/mainte...ce/filters.htm

Oops.... wrong URL

It's http://www.bmwe34.net/e34main/trouble/steeringplay.htm

[EonPeon]

I'm having a bad day!!!!

It REALLY is http://www.unofficialbmw.com/e34/int...placement.html

[baksa]

When I turn A/C off, the sound stops, and it never sounds when A/C is off.
I didn't try to turn volume on stereo up or down, because I'm still not sure if sound is really coming from speakers, but it sounds like it. Never tried it because sound lasts only 5-6 sec.
When my A/C is on, the fan is usualy in 2 or 3 position, sometimes in 4 for a short period, when I want a quick chill in a very hot day. I recently had A/C refilled with gas and A/C oil changed, and mechanic sad that it is working very well,inspite of years.
I also didn't try lowering fan speed.
They also said that microfilter is OK, but in that moment I forgot to mention to them that I get this sound because I didn't think this is A/C connected.

[632 Regal]

its over charged or you have a slight blockage such as the filter dryer.

[Scott C]

its over charged or you have a slight blockage such as the filter dryer.

By any chance does it only do this when the car is hot and the air temp is pretty hot? Reaon I ask is that my aux fan shakes my car (I probably overtightened the hold down grommets)... And since I never had a working aux fan for the previous 4 years, I was shocked at how it rumbled the interior....

Scott