Has anyone noticed a weird sound coming from the engine compartment...more specifically the front left (when facing car)? It's a vacumm'y pressure release sound (somewhat high pitched hissing) that happens intermittently a couple of minutes apart.

I've read some other threads on 'weird sounds' in the past: http://www.bimmerfest.com/forums/sho...ighlight=sound

But this sound is different. ..I don't think its the one described in the above thread related to the door locking (its not a swoooooshclick)....Maybe it could be the fuel pump priming discussed. Anyone know where the fuel pump is located in the engine compartment?