Had a humming noise in my 07 yukon denali that started at 55 and continued to about 80 then would vanish. vehicle had about 35,000 on it when this started. Dealer told me it was an unbalaced tire, etc Blah blah blah. I continued to drive it and the condition got worse. Had a friend look at it that is a racecar builder and he found that the U joints were shot. Took it back to the dealer and they looked and agreed. Replaced them and the humming was gone. I'm now at 82,000 and the humming is starting to return. I think that this vehicle is going to be a U joint eating machine. I think the cause is a combination between a lag going from 4 to 8 cylinder mode that shocks the driveline, and a clunky 6 speed tranny. I have so far been less than impressed with my Denali. I have a stack of work orders two inches thick. I am a traveling saleman so I put on mostly highway miles. The vehicle has never been off the pavement.