I installed a Dirty Air ride system. When I air it down to around 75 psi and lay on throttle a get chatter out of what feels like the drive belt. Chatter goes away when I pump up to 80-85 psi. When aired out does this change angle of swing arm and cause belt to become loose?

 

yes the change in air pressure changes the ride height which changes the anlge of the swing arm and belt tension as it moves, simple geometry. adjust the belt tension to where you'll keep the ride height.