I have woofer pumping too. My TT is well isolated. Although it is very near one of my speakers it is on a sandbox. I tried an experiment, bought a cheap very long cable, and put the TT in another room. It didn't help at all. The thing is that the pumping I get is different depending on the record being played. My solution was to stop worrying about it although the KAB rumble filter does look tempting - do you put it between the phono stage and the amp?
DS
DS