I had the same problem; On some of the year models, the belt has been longer for some reason. I have replaced the belt several times, and the pulleys, and still would get noisy shortly after changing parts. The tensioner did not maintain enough tension, because the belt was longer than necessary. Researched belt length, and it needed to be about a 1/2" shorter for the tensioner to work properly. Looked up a belt for an earlier model envoy and it showed a shorter belt for that one, with the same engine. So I got the shorter belt and put it on in place of the one it called for, and tighter tension pressure and no more noise. It has been 6 months and the car is still doing good. No more comebacks.