I just purchased a 2004 Trailblazer LS 4x4 with 88K miles. No sooner than I got it home, I noticed a rattle in the engine compartment. It seems to be at it's worse when the A/C is on. After inspection, I was sure it was the tensioner pulley on the passenger side of the motor because that is where the noise is comming from. I replaced it and I still have the noise. It sounds like the power steering pump, so I took the belt back off and tried to spin and wiggle all the pulleys under the hood and all are nice and tight with no noise like you would expect if bearings were going bad. So, with the belt back in place, I started it and listened with a screwdriver like a stethascope. I hear the rattle in both the power steering pump or the timing chain cover. I have an extended warranty that will cover the timing chain if that is it, but I want some opinions before I take it to the dealership. If it is the timing chain, is this a common problem? Any help would be greatly appriciated!