How much fuel was in the car? The pumps are in the tank so if you running on vapors the sound isn't as silenced as it would be with pump submerged in fuel.

 

I agree. If the tank was less than 1/2 full, the fuel pump will be above the fuel level and WILL make more noise. Try filling the tank up first and see if the noise goes away. Maybe the noise has always been there but was masked by a fuller fuel tank.

Does the whine occur only when the car is moving? And at what speed does it whine? All speeds?

 

Is it constant or does it come and go as you turn corners? If constant, :iagree: it could be the fuel pump. If comes and goes, it could be in the differential. Have you had the differential noise TSB applied yet (involves draining the fluid, putting new fluid in and adding a special LSD additive)?

 

If problem continues change out your diff fluid. Have you changed it at all?

 

I had the same problem, mainly in reverse but noticeable forward as well. Took it to the dealer and they changed the differential fluid and the problem was gone. This would be my guess with the info you provided.

 

Seems like a pretty common problem, makes you wonder why they don't change the fluid prior to leaving the factory. Save some valuable time and $$ the dealers need to bill GM with.

 

What was the problem? Did you find it yet?