I was driving today in heavy rain and in order to keep the windows clear, I had the climate control on Automatic with the AC compressor on. Noticed a whirring/whistle sound that occurs, and it's definitely not normal. The noise varies directly with the engine rpm and occurs ONLY when the compressor is switched on. I was easily able to duplicate this also in Neutral which tells me it's related either to the AC system or the belts. No undue clattering or other noise, just a hollow whistle.
The AC system still cools fine but then again, it was colder outside the vehicle than inside. However, my impression is that cooling is sufficient. The dealer did suggest replacing the drive belt a few days ago, stating it was cracked. However, could the AC belt also be a culprit, since it only occurs with AC on?
This shouldn't be too hard. Ideas?