i've the same problem on my 04 denali xl. according to my dealer, whom had contacted gm with this problem, they said that it's normal noise on the denali line. the noise is coming from the transmission. it's frustrating to hear that there's nothing that they can do to solve the problem especially for 50K vehicle. when i have my vehicle on cruise control though i don't hear the noise. do you notice the noise when you're in cruise control?