Can low gear oil in the front diff cause a whining noise?

What is your question?

I just replaced the right front hub and bearing because it was making the bad bearing noise but now I am hearing a whining noise at about 30 mph and up from the right front so I checked the diff level and it's a little less than half.could that be the whining noise? Also when I got the car the left rear axle was bad so I replaced it but neither the old axle or the new axle had the retainer ring so the axle pops out sometimes but I can't find one to purchase...maybe you could point me to a site that would have it.thanks for your time in advance.

What makes this problem better or worse?

The pitch of the whining changes with speed

How long has your 2001 Subaru Forester had this problem?

4 days