So the 401 is my rear differential makes a whining noise when brought up to speeds around 20 mph. it also likes to "clunk" at times. The whine I understand would logically come from bad diff fluid, or lack thereof. would pulling a differential off another legacy outback of the same year be a route to go if I don't want to risk draining and replacing fluid to find out its trashed? I would love to hear some opinions!!

The whine and clunk in the diff usually comes from worn ring and pinion teeth or carrier bearings, or both. Best and easier to replace the whole diff with one of the same "gear ratio".

Replacing parts inside is time consuming and if not adjusted correctly you will end up with the same thing you have now.

Try these sites and find one close to you.

car-part.com

hollanderparts.com

kyotomojo101,

When you don't give us the year, model, and mileage of your car the answers you will get will be either none or a crap shoot. You really tie our hands without the information.