Check differential fluid?

Can you check the differential fluid in a 96 lumina? (only 32,000 miles) I'm getting the same kind of whine from that area of the engine as you would hear from an old rear wheel drive car with a bad rear end (not as prominent but the same singing). I only get it when there is a load on... like giving it gas or letting off the gas. You don't hear it during the second when you let off the gas and the load changes from positive to negative. You can tap the gas pedal and hear the whine start and stop as you tap.

Thanks
Johnnie

It is part of the transaxle.