2002 Subaru Forester with grinding noise and banging from back end, and occasional surge/power drop. Is this a differtial, wheel bearings or some other problem?

2014 SUBARU FORESTER REAR WHEEL BEARING HUB REPLACEMENT
https://www.youtube.com/watch?v=LMY8tC4a_64

https://www.youtube.com/watch?v=wUeGcXKPVJg
Some experiences I have had.
If you are lucky I have had rocks get in the tire tread and it would make noise while going down the road.
You may be able to jack up and spin wheel and see is you have the rough noise of a wheel bearing.
https://www.youtube.com/watch?v=sT6tIIvutQc

You can have worn bearings on the pinion gear and/or worn universal joints.

All models are about the same as far as the front wheel bearings go, so go to this link for a how to on the replacement of the front hub.

Possibly brakes not re-installed properly or if bearings were real bad it could be a worn out axle....

Manual or auto trans? If manual, check fluid level. Grinding noise could be u-joint starting to fail, or even wheel bearing.

the front drive couplings are worn this is not serious so as long as the rubber boots are intact and not split just ignore the noise till it starts making the noise in the straight ahead position

I would suspect wheel bearing first
Test just like the front
Wheel off the ground
grab the top and bottom of the tire and rock

However...If I remeber correctly the rear uses axle bearings which are pressed on and difficult to diangose

Therefore... I'd advise you seek a Subau dealer since so few tech see a Forester even once a month

Hello,
Noise can be also from some sticky brake pad, or the bearings of the rear wheels, or even some spoiler, but you should have noticed it right after installing, and it is another sound. As for the differential, there might be a broken tooth, or again bearings, regardless of oil state.

You should have the drive axles checked. Also Wheel bearings. Are there any vibrations or pulling?

If the clacking noise gets louder when turning its the drive joints at the front wheels