'00 300M Belt Tension Bearing
 

I've a suspicious dry bearing sound from the engine. I think it's the Belt Tension bearing. Are they replaceable or the whole assembly need replacing?

That black idler pulley is available at parts stores now. Bearing is made into it. You have 2 different idlers on that engine (3.5L) The snall one that runs the alternator belt is usually the one that goes bad (serpentine)