When I let off the gas pedal it stops making the whine noise, I am assuming it's the differential. I made an appointment with a local shop that does rear ends for Monday, hopefully they will tell me the truth, that's why I came to you guys first.

I found a few other forums here about this same noise and people replaced their rear differential under warranty, too bad mine is older than 8 years, but has less than 80k miles! Oh well, I really love my car. I just wouldn't want to spent 4-5k on a brand new rear end