Whining rear end

[provin1327]

So I have a 1996 Impreza outback 2.2L 5 speed with 180,000 miles. Due to the previous owner not maintaining the fluids and running the transmission low on gear oil, the center differential is going bad and is binding up on tight turns after it is hot. Because of this I am no stranger to loud and clunky diffs when it comes to this Subaru. I am waiting for the weather to warm up to replace the center diff but I think I have a new problem in the rear.

 

I drove home from work today and noticed a new whining/jumping noise on deceleration, keep in mind this happened before the gears were hot at all, I could hear it when leaving the parking lot. I have been hearing a gear whine since I purchased the Subaru about 4 months ago but this new noise is much louder. I am not sure if it's the center diff that is making all this noise or that maybe the rear diff and center diff are both going bad with the center diff locking up and the rear diff making all this noise. The noise is at its worst around 40 mph and then at highway speeds. It's also loud when in neutral or decelerating while in gear with a spike in noise around 40 mph. I also went to check the rear diff fluid and could not get the fill plug broke lose. It looks like it's a bit stripped or that the previous owner had the same problem and messed up the plug a bit. Fortunately for me I did not remove the drain plug before the fill plug. So that little piece of evidence also has me worried about the rear diff and if there is even any fluid in there .

 

I need advice as to what to look for or if I can test anything on the Subaru to confirm where this noise is coming from. It sorta sounds like it's coming from the rear but I can never be sure with noises resonating through the drivetrain and cab. Should I jack up the rear end and turn a wheel by hand and listen? Could it be a bearing in the rear end that is going bad? I am guessing it is gears because it seems to be directly related to throttle and coasting, i.e the drive or coast side of the gears may be messed up, warped, etc. I have already pulled a center diff from the junk yard but I am considering making another trip to the junk yard for a new rear diff. Any advice on this? What about gearing, I don't want to pull a junkyard diff and have it be the wrong gear ratio. I can't find much info on replacing the actual differential, lots of videos on replacing fluid . Is this a time consuming job?

Edited April 4, 2014 by provin1327

[nipper]

Rear wheel bearings. Check rear diff fluid level. Rotate tires one side at a time and see if the sound moves with the tires.