Rear end noise decelerating OB, MT

[pcwizard2600]

I have a 98 Outback wagon manual trans. that suddenly developed a noise when decelerating in gear (so there is a load on the drive train). Quiet accelerating or when coasting with the clutch pushed in. Does not change moving side to side. Sounds like it is coming from the rear. Kind of a deep whine or howling sound. This was not gradual, just started all of a sudden. I'd relate its symptoms to an older rear wheel drive car with pinion gear/bearing problems. This is a higher mileage,(122,000) maintained vehicle. I haven't had a chance to get under it yet to start troubleshooting it, but any thoughts would be appreciated. Also wanted to add that there is no noticable vibration with this yet, and nothing related to the brakes either.

 

Thanks