I recently installed a 2 speed pump and have noticed when I'm done manually vacuuming and turn the pump off there is a noticeable "thump" sound coming from somewhere between the pad and the pool. I can also "feel" the thump somewhat.
I tried going from high speed to low speed to see if that made a difference and it still makes the noise. It only happens when vacuuming, not during normal operation.
My psi is normally around 18-19 psi and drops to 13 while vacuuming on high speed. The two suction lines are 2 inch pipe and one return is 2 in and the other is 1.5 in.
Any thoughts on what the noise could be?