Remove both pulley covers and visually inspect for wear on inside. You might find debris between pulley and cover. Remove belt and inspect for wear, cracks, etc. If belt looks good and inside of covers look good, I would clean top of deck, inspect grooves in pulleys for rust as well as sharp edges. A piece of steel wool will get rust out. Check spindles for bearing wear by spinning pulleys and also using both hands on pulley try rocking up and down back and forth. Grease spindles, reassemble and check it out. After mowing, I use a blower to clean tractor off. Water will bring rust to pulleys and other steel parts. Hope this helps, let us know what you find.
