I have a '98 S70 T5. After the car has cooled overnight, the the engine makes a howling noise upon startup. It's barely noticable at idle, but becomes much louder upon driving away or revving the engine while in park. The noise eminates from the passenger side of the engine. After driving for about 1/4-1/2 mile the sound goes away and doesn't return for the remainder of the day. The sound is not like a water pump bearing shriek. It's a lower pitch. Local mechanics have replaced the alternator, power steering pump, and cam belt tensioner to no avail. The problem persists. Does anyone have any thoughts on what this could be? Thanks.

 

What about the Cam belt idler as well?
What about the serp belt tensioner?