That sound for a 968 is the pinion bearing going out on the tranny.
I'm not sure how closely related the 944's is to the 968's.

 

My car has a rear end sound, probably something to do with the tranny. It make a whirrshhin noise if im off the gas and coasting. When i get on the gas it goes away, also goes away if i put the clutch in.

 

Wow, lots of action since I posed this question. Electric motor sounds (hatch release, sunroof motor) make sense as a possible source, but neither of those items are malfuntioning. Car doesn't have ABS, so that's out. Seems to me that if it was a bearing it would be related to road speed or rpm, but it's not. In fact, it doesn't even happen every time I drive the car. I'll have to pay more attention next time it happens to see what else is going on.