Hi all, 

I have a 2002 impreza outback that makes an incredibly loud humming sound in the back while driving. It's been getting worse and I suspect it might be the rear differential. I bought it last year and not sure when PO changed the fluids on it. As a starter, i figured I'd change the rear diff fluid and see what happens - maybe there;s lots of metal shaving on the plug which might indicate some issues with the differential. What i can't seem to find online is:

1) What type of fluid I should be putting in it

2) How much ?

Do any of you have an idea for this particular model ?

Thanks,

Vlad

Bad rear wheel bearing?

1 minute ago, Crazyeights said:

Bad rear wheel bearing?

Perhaps, but I'm not sure as the humming does not seem to fluctuate when i turn left of right , which according to my understanding could be a sign of bad bearings.

+1 on a bad wheel-bearing.

Wheel bearing. Most likely pass rear. 

GD

any way I can check for this to be sure? I m not sure if the humming is coming fro one side or the other. Seems to be somewhere in the middle. 

1 hour ago, vladnedelea05 said:

any way I can check for this to be sure? I m not sure if the humming is coming fro one side or the other. Seems to be somewhere in the middle. 

wheel bearing.

To tell which side - your hunch is probably right. Ride in the back or trunk or have someone stand outside while you drive past them from both sides. Check for play   Or just wait once it’s bad enough you’ll tell.