The pulley is driven by the belt and spins whenever the engine is running. The drive plate stands 0.5mm away from the pulley and spins only when AC is used. The drive plate is attached to the compressor shaft (flange) by 3 springs and 6 rivets. When the AC is turned on, the clutch engages: the magnet in the clutch attracts the drive plate and the drive plate snaps on the pulley and spins with it thus powering the compressor. The springs let the drive plate move back and forth by 0.5mm. The torque is transfer from the drive plate to the compressor shaft thru the springs. When they break, the drive plate sits free between the pulley and the flange. Then it can rattle as the pulley spins but not the flange. If you engage AC with broken springs, the drive plate will start spinning with the pulley and the remaining portion of the broken springs will rattle when touching the non-spinning flange. If your springs are broken, the drive plate will most probably be loose on the compressor shaft held in between the pulley and the flange. You will also easily notice the 3 broken springs.