The timing belt tensioner pulley is indeed a critical timing component. If it fails the belt will likely overheat and jump/shred before you realize what's happening and can shut the motor down. It will destroy the motor.
It may be a power steering or alternator bearing, drive belt pulley, water pump (or something else all together), So as suggested above it will need to be checked out by yourself or preferably a competent tech, and right away, because of the risk involved if it's the timing pulley.

One thing to consider is that the timing tensioner pulleys on these models ('99-'00) are known for premature failure. I Believe the timing belt is even sold in kit form with tensioner upgrade, and is "must" for replacement with the first timing belt. I think the service interval for the belt/tensioner on that car is 105K, but I've heard of early tensioner failures much sooner.

Don't dick around with it. Find out what the noise is. Hope it's something simple and non-threatening.
Let us know what comes of it.