RJC

I just began hearing a humming/buzzing sound coming from the engine compartment when the A/C is on? Seems to either be there all the time or just when turning a/c off. Sounds like its coming from the A/C compressor. I posted more details in the tech section but please post your responses here.

Thanks all.

Eich

It could be the secondary radiator cooling fan coming on when the engine is hot and the AC is on. I used to think my AC compressor was making noise until I figured out it was the cooling fan. This car has the absolute loudest fan I have ever heard on any vehicle. Outside of the car it sounds like a jet landing. Inside, I hear a grumbling sound and the car shakes a little when I'm sitting idle.

I understand there is a tech service bulletin for this where they reduce the speed of the fan. I will have this done at my next visit.

RJC

Thanks Eich. The noise is from the A/C compressor (I put my head as close to the compressor as I could and the sound seems to be there) when I turn the A/C off the noise stops but the cooling fan keeps running at a constant speed. I made a post in the tech section a Patrick an MBTech in Europe said there may be an issue with this new type of compressor (clutch always engaged and an electronic valve controls things). My A/C is nice and cold but the noise is new and dosn't sound right. I get a vibration from the cooling fan too when its running fast, that can be corrected by better securing the fan shroud/housing (my dealer did this on my 03). If you check you'll see the fan assembly is a loose fit not very secure at all and that's a big part of the vibration.