Strange subsonic rumble problem?

Hmm.... I have 2 arms on my TW Acoustic Raven AC, a Reed 3Q and FR 66S sitting on Minus K platform. Yesterday, I took out my Koetsu cartridge and put on Ikeda Kai on my FR 66s. After the usual setup routine, I noticed significant subsonic rumble with the woofers pumping like mad when using the FR 66s. No such problem when using Reed arm playing the same record. I never had subsonic rumble problem in my system for a long time now and no problem with FR 66s in the past. The setup seems to be fine, all the joint, screws, etc are tightened properly as far as I could tell. Overhang, VTF, VTA, etc has all been checked several times so I am out of idea now what else to check to eliminate the problem. I assume airborne vibration, acoustic feedback should not be an issue since the problem was not there before and the turntable sits in the same location for years now.
Thanks for any suggestion.
That resonance is on the low side close to record warp frequency! Nine times out of ten this will cause woofer pumping. You should get a good test record so you can see this for yourself.
I use Shure ERA 1V TTR115 test record, it is invaluable for this test.
You can find them on Ebay for about $20.00. It would be a wise purchase for someone like you who is into vinyl.
Maybe that arm/cart combo does not like that record? Does it do it on other records? If so, you may have a problem with the arm.
have you checked if your FR66s arm is properly grounded?
Sarcher, it happened with every LP and Reed/Lyra did not have any problem with rumble on any of those LPs. Anyhow, for some reasons, the rumbles all disappeared today. All I did was taken out the phono cables from Audio Tekne and and plugged it directly into my Thoeress phono instead (mainly because it was a lot faster to turn on and off and I don't have to wait as long in between while I tried to fidget with the arm/headshells etc. Go figure, don't know what is going on but will try to plug it back into AT SUT/Aesthetix later.

11flat6, not sure what you mean by teh arm properly grounded? As in the ground lead on phono cable?

Yogiboy, I do have a few test records, if the prolem recurs, I will verify it with a test record, thanks.
Hmm. I guess it's just a bad connection. I would not think that would cause woofer pumping. Could be something is causing the preamp to go into oscillation? Maybe someone with more technical background could elaborate?