#15131
JohnDisney
Participant

    I had a similar problem on my B32 and found the pump was leaking from loose fixing screws at the joint below the motor and the diaphragm. As a result it was sucking in air which caused the knocking. Tightening the screws, which you can see in your picture at the bottom, solved the problem. The vibration of the pump operation causes the screws to loosen over time.