My only guess, is that the motor is out of alignment with the pump. Actually, if you can dig your way down there, you will see the static alignment, the carbon ring, with the opposing stainless sleeve, should be against each other almost within a mm if the circumference. I assume the bellows are secure, and there are no cracks in the bellow, or, perhaps, the bellow has lost its expansion push against the steel sleeve. A misaligned motor (over time ), often can be the culprit.