serpentine belt tensioner

Think what you will! My LC 200 y 2000 284k has been low humming,for 2 years but voltmeter showed new battery and old alt doing just fine at 12.+ Cold and 14.+ With engine on... All the way to this morning! 2 mechanics 2 yrs ago at maintenance said they couldn't hear the low hum nor replicate...

The bearing on the engine fan of my 2003 LX470 started to make noise, and actually gave out while I was showing it to the mechanic. The mechanic replaced both the COOLING FAN MOUNT SERPENTINE BELT TENSIONER though I don't know if the serpentine belt itself was replaced. I've just called and...