I own a 98 S70 and when I start the car up, particularly after I have not driven it in at least 8 hours, I get a high pitch "fan" sound that resembles a vacuum cleaner starting up. Sometimes it lasts 10 seconds, sometimes 30 and even up to a minute. Then it powers down, which sounds like shutting off a vacuum.

It is very loud and distinct and given the fact that it only happens after I have not driven in awhile, I wonder if it is something warming up in the car? It will usually only kick in when I start moving the car, and it only does it once per "session" of driving.

Does anyone know what is making this sound and if it requires any attention?

 

Found a video that someone posted with the sound that my car is making:
0316091653.mp4 video by cabbott709 - Photobucket

Looking into this further is leading me to believe that it is a bad air pump and check valve.

For anybody having the same problem, it is an easy repair, but the parts can be expensive. The cheapest air pump I've found was $330 and the check valve will run about another $100

 

Volkswagen uses a similar pump with slightly different mounting plastic parts. I've seen a write-up of the guts swap, but can't remember the location. Don't be averse to hitting up the junk yards.
Ed- Chicken Engineer, Mississippi State '88

 

Good call, will probably hit up the junkyard after I fix my axles/hub bearings

Here is a good thread on this topic (bad air pump noise) for reference if anybody needs:
98 S70 Makes Weird Noise - Volvospeed Forums - Page 2