Why are my woofers pumping?

@o_holter Reading over these posts I'd lean toward motor, pulley or bearing as the source of the problem.  By way of example, a couple years ago I noticed excessive woofer pumping in my speakers.  It was extreme to the point where I could hear chugging from my subwoofer.  I have a VPI HW-19 Mark IV with a very early SAMA.  The early SAMAs came with a flywheel that was a large stainless steel washer that just slipped over the motor shaft.  Upon examination I noticed that this "flywheel" was wobbling while the motor was running.  I removed the flywheel and the problem was solved.  I later learned that VPI eventually realized the flywheel was causing more problems than benefit and discontinued using it.

Since you observed much less pumping after removing your platter it sounds like either your platter was out of balance on the bearing or the bearing was not properly seated.  I would clean the bearing shaft with long qtips and reoil the bearing shaft with a high quality oil.  I use sewing machine oil.  Second, I'd examine the pulleys and motor shaft for any wobble.
Cheers,

@o_holter The studder you are seeing in the spindle is typical af asynchronous motors and not a malfunction.  Download and read the manual for the VPI HW-19 MK 4.  There is a paragraph that explains this.

If your woofer pumping returns do not use a filter.  You would just be covering up the problem instead of solving it.

in the meantime, enjoy the music.

@o_holter I must echo armasphere.  Pumping once per revolution is not electronics.  It has to be bearing or platter related.   It acts like a warped record.  Have you checked to make sure your platter is dead level?  Put a small bubble level on the platter and turn it slowly by hand to see if it is level through a complete rotation. Repeat this with the level in different places on the platter.  Don't use one of the small round levels supposedly designed for turntables.  Use a fairly short (6 to 8 inch) carpenters level.  Second, have you checked to make sure the platter is not wobbling on the shaft?  Good luck.

@o_holter  Well, I don't know it is the TT as opposed to a warped or otherwise flawed LP.  If the pumping is being caused by the record I can think of only 2 issues: 1) The records are warped or otherwise flawed and you're not going to solve that problem by making changes to your system; or 2) Your system is so resolving at subsonic levels that it is reproducing subsonics that were present at the recording venue.  Once again the problem would not be your system.  I don't recall the LP but I have one where I can actually hear either a subway or air conditioning system on the record.  

Since, however, you have mentioned several times that the pumping occurs one time for each revolution of the LP it would seem an amazing coincidence for you to have that many warped records or that the signal recorded on the master was exactly in sync with one revolution of your platter.

@o_holter Very interesting, your last few posts.  I have noticed on some LPs there can be a hum in the runout grooves and have always supposed it was on the record.  I don't see why there could not also be subsonic signals in the runout grooves that would cause woofer pumping also.  Unless the woofer pumping is extreme I'd be inclined to congratulate my self on a great resolving system and ignore the pumping.  If it is bothering you, I suppose you could use a subsonic filter as some here have suggested.  I personally don't like filters because you are just placing additional things in the signal path and more "stuff" you put in the signal path the greater the opportunity to degrade your sound quality.