I think it's a tensioner or idler pulley. The tensioner itself might be fine...see if the belts are running flat between pulleys. If the belt is hopping, the tensioner isn't good.
No one that I recall in an ordinary non-M, non-turbo e46 has had an issue with timing chain tensioner/guide. I'm sure someone has, but they probably have over 200K miles at least or been doing stuff to engine.
If one pulley is bad, replace all three--make sure you know what tensioners you have before you order pulleys.
Oh, use a hose as stethoscope and verify the source...or remove belt and spin pulleys...if it spins freely, it's bad. It should stop in a rotation or two. Anyway, at that point, I'd just have them handy and replace them...and belts. Autozone sells dayco pulleys are are OE (INA brand) if you didn't know.
Search pulleys in thread titles...you'll find out all you need.
In NJ--Tierney's in Montclair, Sept. 25, 7:30 p.m.
In NYC Sat, Sept. 30, 8 p.m. at Broadway Comedy Club! Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Comedy can be a great cheap date!
Mangofy your E46!