Subaru Problems? Ask a Mechanic for Answers ASAP
What type of fluid was used in when you changed it? Synthetic, conventional, what viscosity?
If synthetic 75w90 wasn't used you will definitely get a noise.
Also if the tires are different at all it can not only make a whine noise, but I have even seen them blow out the differential if driven enough. I had a customer replace only the front wheels of her subaru and left the rear wheels because they were only about 60% worn. It caused so much heat in the differential that it melted all of the seals out of the differential and melted the rubber mounts that hold the housing.
I would make sure that all of the tires have the same tread pattern and then I would take a string and measure the circumference of each tire. If one or more tires is off more than 1/4 inch from the rest, it needs to be replaced.
I just wanted to see if you need any additional information.
If not, please don't forget to rate.