My 2000 with a 3.8 has been making noise fora while now. It is coming from the serpentine belt or tensioner I'm guessing. The belt does not squeal but it's more of a light rattling noise. I've changed the belt 2 times and each time it will stop making noise for a few days then it comes back gradually. I've changed the tensioner 2 times andeach time the noise will go away for a few days then come back. If I spray silicone onto the the belt at any spot on the belt the noise immediately stops but will come back again shortly thereafter. When I have the belt off all of the pulleys seem to spin freely without any wobble or freeplay. Any ideas? Thanks.

 

Are each of the pulleys aligned? Silicone will reduce the friction of the belt on a pulley and as the silicone wears off a mis-aligned pulley may make bearing noise in the component (alternator, compressor, etc). Just a guess.

 

Thanks. I'll check them. I didn't check that specifically but during my close inspection of each individual pulley a misalignment problem didn't jump out at me.

 

Does yours have an Idler pulley, mine did and was bad. $20 from the dealer, vs $29 from a National chain... up on top of the engine and easy to get to... mine's an '03 though...