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
Cool responds. I am only using Thorens weight at the middle. Most of my LPs are used so the arm is moving up and down some times! I will have a look at rings and weights than. Thanks.
Rodman, Thanks for the info. Very useful! Ah.. Has anyone used those heated device to flatten a wrapped disc?
They do work, but- the good ones are not cheap, timed cooling and all that: (http://drhifihousecalls.com.au/New%20Equipment/Furutech/Furutech%20Record%20Flattener%20DFV-1/Furutech%20Record%20Flattener.htm) It can also be done, in the oven, between two thick pieces of glass(with extreme care). (http://www.radiodismuke.com/forum/index.php?showtopic=670) Happy experimenting!
BTW: I think someone mentioned this, but- a record weight(just in the middle), will cause the circumference of some thinner vinyl records to lift off the mat. If there is an acoustic feedback issue, this will exasperate it. The one mentioned by Ct(with the black felt washer under the label), addresses that nicely, as long as it can clamp to your spindle. Mine is tapered, and I have a thicker than stock mat. I can't use a center clamp, as a result.
Someone might want to ask Luna if his speakers are ported.

Oh, Luna: Are your speakers ported?

If so, do yourself a favour and buy the KAB. Your speakers, your amplifier and your ears will all thank you for it.