Woofer sucking in and out


I have a problem with my analogue set up that once it starts play, the woofers of my speaker will move in and out like crazy, unrelated to the music! It relates with volume as when the volume is low, the woofers will not move as much. May it has to do with oscillation between cartridge and arm but my set up is new. The turntable is Acoustic Solid-Transparent and rega301 arm with cardas wiring and weight mods, Herron VTSP 3A pre and VTPH phono. I wonder if placement has anything to do with it or power connection.
I hope someone who has the same problem before can give me some hints.
Thanks.
luna
It made sense as I have only moved the set up to the location next to one speaker on the side wall lately. It was between the speakers before. I thought equipment on the side is better than in the middle. I will try to move them back. I was thinking the tubes has gone bad or something? Thanks for the help and I will get back when I have some progress.
Your idea is good, just happened that it brought about another problem. I've had things like that happen ever since I set up my first system.

If you don't make some mistakes you're not trying :^).
My turntable, a Dual 1219, was into woofer pumping too. Search A-gon's database for that and you may find more discussion. You're far from alone.
There is absolutely nothing wrong with equipment being in between the speakers. 99.9% of systems are setup this way. Of course, ideally, the speakers should be farther out in the room than the rack the equipment is on.

I suspect, as others have said, you have an isolation problem, or a mismatch betweem arm and cart.