Serpentine belt is clean. Upper pulleys look solid. This is just a stock photo so I could show it clearly

 

Probably belt tensioner has lost its spring tension. Belts get glazed from slipping also not to mention WD is bad for the belt. Take the belt off and check / spin all the pulleys for play and noise. Check the crank damper for the rubber ring in it failing. If everything else checks good replace the tensioner and belt. They are a ''set''.