I used to have the same problem, it is NOT normal, after reading many discussions on this in this forum web site, I talked to my dealer and he ended up replacing my rear end and the whining noise is gone. My concern is will it return with the new rear end since my first one didn't start whining until I had around 1600 miles on it, (currently have 1200 miles on the new one). I asked the dealer what the root cause was, he didn't know. He said there have been enough complants that GM will replace them within the warrenty period. So hopefully GM knows what the root cause is and is properly implementing the design or manufacturing fix in the replacements.