The pulleys all have to be rotating in the same plane. If one is out of alignment it'll cause noise and accelerated wear eventually throwing the belt. Remove the belts,spin the pulleys and check for any roughness in and excessive side to side play in the bearings. Check them for coplaner with a straightedge across adjacent pulleys. Check all pulley combinations with the straightedge. The belt tensioner needs to be checked for tension and smooth swing with no binding. Make sure the tensioners pulley isnt cocked and the belt wear pattern on the pulley isn't alot wider than the belt itself. I see that as a very popular problem. Most tensioners have a wear indicator on them where the line on the swing arm has to be in between two lines on the stationary part bolted to the block when the belt is installed . HTH