This is driving me crazy. On my '07 4.8i, I have a belt squeak when warm. It chirps a little at idle and squeals past 1k or so RPM. This noise has been present since I bought it and hasn't gotten worse or better as I've driven it during the past year. I figured it was just an idler pulley going bad so I replaced the main belt, a/c belt, the main tensioner, idler, and the a/c tensioner (the manual one). I want to say I spun all the accessories by hand when the belt was off and they seemed fine; the water pump especially looks new although it was replaced prior to my ownership. With all that replaced, it was *still* making the same noise - so I replaced the a/c "clutch" bearing with a new NSK bearing. And it STILL makes the same noise! Any ideas? Is the a/c belt directional (I think I read something about that, but don't recall seeing it mentioned in TIS when newTIS was still up). What should the tension be on the a/c belt? I had it close to what the main belt felt like and I just cranked the tensioner down today. It seems a little quieter but also feels very tight and it's still making noise with revs.