Lower deck to lowest setting, hands on, check idler pulleys for sloppy play. You may have to remove deck to check idlers, try rocking them back and forth & up and down, try spinning pulleys are they smooth or rough, bearing noise or not. Also check spindle pulleys same way. Make sure all hardware is tight and secure.
If you have idler arms check to see if they are cracked and move them up and down checking for play. Let know what you find.
