Chasing down a squeaky M104.980

[John5788]

I've been hunting a squeaking sound from the front of my M104. I thought it was the water pump and I replaced it only to find that the squeak persists. The squeaking sound is very loud at cold start up, but once the engine hits operating temperature, it quiets down to a small chirp and eventually silence. Applying throttle expedites this process of quieting it down.

The engine serial # is 12-022483 and according to EPC it needs a 2445mm belt. This leads to my first question, what's the difference between the 2 cutoffs that change the belt size from 2415mm to 2445mm? Maybe I'm running the wrong belt length because of the parts I'm using?

Without referring to the belt tensioner indicator, how do I determine if the belt is too loose? The tensioner says it is adjusted correctly (pointer at largest part of the triangle), but maybe the tensioner has failed early? The tensioner is only a year old as is the belt.

Any other ideas? It's not the idle pulley by the exhaust side. I already replaced that with a brand new fan bearing bracket.