^ What he said.
Be sure the tensioner is attached to the timing cover firmly (it's just one bolt, more or less in the center of it. I forget the torque spec for that bolt, but it's not much - maybe like 20lb/ft or something). If it is, and it's grinding up against the timing cover then the bearing/bushing in the tensioner is shot and the whole thing needs replaced. Not a big deal - it's about $35 at Autozone and 10 minutes of your time.
Don't let it rub against the timing cover very long; the timing cover is aluminum and not very thick, and the pulley on the tensioner is steel. The pulley will win that fight, and when it does it will be a much bigger job. When my tensioner went, it took out about 1/16" of material from the timing cover in less than a few minutes.
2001 ***** Slayer Red GT convertible; all of the usual bolt-ons.
1967 Notch; 200 I-6, C4 auto