The car is a 97 C280 Sport, and this started happening about 2 weeks ago. It was pretty faint at first, but has been getting progressively worse.

Only does it when the engine is running, not if the accessories are just on. It sounds like it's coming from directly behind the passenger air bag, as if I put my ear on it, it is the loudest.

I have no clue what it is. It does it with the radio turned off, and the vent and a/c turned off. Maybe some sort of pump?

I did a search but couldn't find anything simliar to this.

Thanks,

- Anthony

 

The only other thing that's behind the airbag on that side is the blower motor. The water drains at the bottom of the windshield are pretty comon for clogging and backing up causing water to enter the blower motor area. If this happens it can cause the blower regulator to short out and allow the blower motor to run when it wants.

I'd inspect it for water damage, but you'll at least need a blower regulator, possibly the blower motor.

 

Bumping this from the dead, but the sound is getting constantly worse and louder.

You really only hear it if you are light on the throttle, or off the throttle completely, or on the brakes. It seems that under moderate/heavy throttle, the noise is gone.

I really can't pinpoint where it is coming from, but man it's annoying. At first I thought it was the brakes, but it's not the right type of sound. This sounds more like an electical whine than a brake squeal.

Any ideas? It does it both when the HVAC unit is on, and when it's off, so I'm not sure if it's the blower motor.

 

take it to a mechnic and ask him. If its common, he will probably just know what it is, if not, he can figure it out im sure. if this is on going from oct 06. get it looked at before it gets mroe exspensive

 

I bet is a vacuum element of the air duct flaps, there's got to be a vacuum leak somewhere, chech that all your air supplies are working correctly in all their positions, probably the vacuum element has a leak or a vacuum tube is loose

 

I had this problem on my C220 when it sits overnight and the engine is cold.
Check your air pump (part of the emission system), that was my problem.