So I installed my stock vlsd diff back into my car and I put the same fuild in my other diff in that diff the other fuild was about 1-2 weeks old so basically new. Drove it for a few days and no problems. But now

When the car is accelerating it has No unusual noise or anything but as soon as you get off the throttle you gear a loud whinnying noise from the back of the car. So I jacked the rear end up and had my gf slow accelerate and them let off and I can hear and see that the noise is coming from the diff. What is the problem? And why is it doing that? Someone have any insight on this and the severity of the problem?

 

Bump got new diff fuild and still nothing