Does it whistle while running or with engine off? If it does it while running then the oil trap box has an internal vacuum leak. It should be posting fault codes for fuel trim problems if this is the case. If this is what you mean then call Volvo to see if the oil trap box is covered by the extended emmissions warranty. Should be covered for 10 years/150k miles. Also if it does whistle while idling, remove the oil cap or the dipstick. You will here a load suction noise and then the whistle will go away. Good luck to you and keep me posted please.

Answered by JIS001 (expert)
1,861 answers provided

My car whistles while idling as well as for a few minutes after the engine is turned off. When I removed the oil cap and/or dipstick-it continued to whistle. There is a small 4-5 inch cylinder shaped part that reads "pumpe UP28" near the battery on the right side of the engine-it sounds like it is coming from that or very near by. The car seams to run fine except the AC gets warm after about 15-20 minutes, I don't know if that is related.
Thanks,
tammichaelson

Response from tammichaelson
1 question asked

I dont think they are related. Your A/C issue will most likely be a worn compressor clutch? As for the whistle sound you may have to take it in to get it checked out? Also just to make sure this is the new style S40?

Answered by JIS001 (expert)
1,861 answers provided