Nelsonjmbf

i have a 2007 E350, i started to get a whine that im pretty sure is coming from one of the pullies, when i check voltage its 14.0 steady so i don't think alt problem, i have new tensioner to install just haven't yet but the other day i noticed belt had slit it in so i changed it an while doing so notice idler pully, which i change when i bought car year ago looks like it needs replacing again, I'm wondering if the tensioner needing replaced could have caused this or if i should be looking elsewhere for root cause? i know very little so any ideas methods on how to diagnosis everything connected to belt system would be lovely.



also, when I try to buy upper idler all i can find is the one in pic with silver cover, but it looks different the one the car has the black plastic piece pictured below that covers screw, does it matter which is used or because I can't find the one with plastic cover.