Sorry the time difference meant I went to bed and didn't see your reply. I wonder if you could do something for me. Make it happens again but this time and it's going to sound strange gentle place a finger on the back of the dry side. Each pump is fine tuned on the assembly line with washers and small weights added. I would be interested to see if the dry side has a twitch during feed mode... Also whereabouts on the power cable is the first sticky support pad? The cable in the first picture looks like it could be aways up the line? So any movement in the pump could act like a clock pendulum.