First time using the mower this year and noticed a squealing noise whenever I engaged the self propelled. I don't recall hearing this noise at all last year and the belt was replaced last year and has no visual wear/cracks, etc. I took the drive cover off to look at the pulleys and thought the one pulley seemed loose but while tightening it I snapped the bolt that goes through it... :( Anyone have any advice how to track down this noise? There are 3 pulleys, and I'm thinking one of them is the culprit but how the heck can you tell which one it is?

I have a Husqvarna 7021RES with the EZ walk self propelled system and here's a pic of the piece I broke off.