Hi,
I've noticed a weird noise emanating from my 1992 900S, which only occurs when the AC is switched on. It's a very low-frequency throb, which is only noticable when the engine is at an idle (at which time it is actually sort of loud in the subtle way low frequency sounds can be loud). It is sort of rhythmic, but does not really correlate with engine speed. The engine idle speed (the usual
800 or so RPMs) remains perfectly steady. My AC system just had some work done on it, actually (replacement of hose from compressor to receiver/dryer, and receiver/dryer itself), but this noise was audible before that also. The AC seems to be working fine. The noise is more noticable from inside the passenger compartment than it is under the hood/bonnet.Any sugggestions?
Thanks, John