Thanks. My S40 has 115k miles, so I better get this sorted out soon.

Should I be able to hear the "whistle of death" immediately after starting it, it does it require driving for awhile? When I thought I heard it last night I'd made a brief trip (2-3 miles) then went back into the house with the engine running; when I came back out i thought I could hear a whistle or whine, but I wasn't sure. Just now I went and started it and opened the hood, but couldn't hear anything.

 

It was faint on mine. Open the oil cap with the car running. If there is pressure or a lot of suction, the PCV system is suspect. A dealer can diagnose. If it's not the PCV, you'll have to pay the diagnostic fee. Small price to pay considering the damage excessive pressure from a bad PCV can do.

 

I have the same issue with my S40 2006. I remove the oil stick and the noise goes away.