Are the pullies all in line together ? Did you change a blower pulley and make sure it's fully seated ? Lastly and more than likely the belt tensioner in not good , I would buy and replace the tensioner and this should solve your problem
Sent from my SM-G955U using the svtperformance.com mobile app
Could be an idler bearing issue. Hard to tell without hearing it.
Did you spin the idlers by hand with belt off?