Low frequency problem while playing vinyl

Has anyone experienced (and knows a cure for) a very low frequency problem while playing records. Just recently I hooked up two old turn tables, Linn LP12 (1980s) and Dual 704 (1980) in my system and the woofers of my speakers are almost jumping out of the speaker cabinets while I am listening to a record. Displacement at least 0.5 inch if not more and the keep "pumping". Needless to say that I didn't experience this issue years ago when I used to play records regularly.

amps: Krell Ev202/350MCx
speakers: Thiel CS7 + smart sub
phono amp: Valvet
If the bass output continues to increase into a 'roar' forcing you to lower the volume, you are experiencing acoustic feedback. This happens when bass energy from the speakers is coupled back into the turntable/arm/cartridge in a type of feedback loop that grows upon itself. It can be difficult to address but I would start by attempting to better isolate the turntable. What is the turntable currently placed upon? You can experiment with alternate bases for the table, and possibly a wall mount turntable shelf.
Were you using the same phono cart with both TT's?
It isn't acoustic feedback as I had the same problem. After trying everyone's advise here, I bought a KAB rumble filter and it solved the problem. It goes on a tape loop and it does not take away any bass, just the oscillating.
It could be arm and cartridge mismatch. Resonating above 12hz.
Dirty bearings? Warped records? London recording of Tales of Czar Saltan?
Most full function preamplifiers had rumble filters built in to phono stages back when everyone listened to vinyl. Glad you got it sorted
Here's a test, with the turntable off, not rotating, place the cartridge on a record. Slowly advance the volume to the level that you commonly listen at. If howling begins, back off. You have found out that you have a problem with acoustic feedback and if it is structure borne, you will have to change the structure on which the table sits. If it is air borne, you will have to site the turntable somewhere else.

This is usually only a problem with vented woofers, which are unloaded below their primary resonance. Acoustic suspension woofers remain loaded and will not show this kind of response problem.
Rumble or not, it's still feedback. The primary issue is not on what, but where the tt is placed in relation to the speakers.
Thanks for your responses. I did some more testing to locate the problem. The low frequency signal seems to be generated by the phono pre amp (VALVET soulphono MM/MC tube phono amp‏). With the phono pre amp hooked up to the pre-amplifier (Krell Evolution 202), without the turntable connected the woofers go crazy when I turn up the pre amp volume.
I suggest getting rid of the problem rather then covering it up with a filter. Linns do best on very lightweight small tables ( probably the Dual too). The next thing to think about is the cartridge/arm compatibility..you don't mention the arm or cart. A major mismatch here would actually make the cartridge mistrack you don't mention that. These large subsonic excursions are caused by waves...many times the front of your supporting table will move differently than the back. If your table that supports the turntables are close to the wall, either anchor the table to the wall, or put a prop between the table and the wall to prevent the table from moving inappropriately....I would try these things first before clamping down your system with a filter.
The low frequency signal was generated also with the turntable disconnected. I have also never experienced this problem before (without Valvet Soulphono).
I'm not sure what the solution might be, but given that both your preamp and your amplifier have specified 3db frequency responses that go down to an extremely low 0.1 Hz, and given that your amplifier is very powerful, I suspect that the explanation of what is going on may be what Atmasphere (Ralph) described in this post, and his next post in that thread. Except that in your case the low frequency instability he refers to is presumably in the power supply of the phono stage, rather than the power supply of the preamp.

In that thread, the problem disappeared when the load impedance seen by the tube-based preamp was reduced from 100K to 47K, for reasons that are explained in Ralph's post. Although he felt that was not a good long-term solution, as an experiment you might try reducing the load impedance seen by the phono stage.

I see that your preamp has an unbalanced input impedance of 47K. A convenient way of substantially reducing the load impedance seen by the phono stage from that value, as an experiment, might be to use y-adapters at the outputs of the phono stage, and routing its outputs into two components at once. If you have some other unused component handy that has line-level inputs having 47K input impedances, for example, having the phono stage connected to both components at once would reduce the load impedance it sees to 47K/2 = 23.5K. The second component needn't even be turned on, or connected to anything else.

Alternatively, you could solder a couple of resistors onto RCA connectors. Or perhaps find online an equivalent termination that is already prepared, that you could order. Something like 10K might be a reasonable value to try.

If that eliminates the problem, while it wouldn't be a suitable permanent fix it would provide confidence in the explanation. The explanation seeming particularly plausible in this case, as I said, because of the extreme low frequency bandwidth of the Krell components, coupled with the high power capability of the amplifier.

Hope that helps. Regards,
-- Al
My pro-ject Xpression III had this low freq response proem with pumping woofers. I first tried using the subsonic filter on my pro-ject tube box, it helped a little. It also reproduced when I upgraded to a new jasmine phono preamp. The problem finally went away after upgrading my table to a new RP6. I guess some tables have this issue and some don't, depending how well the motor is mounted and isolated and how well the table is designed, including the arm.
Also forgot to mention both tables were used on a rigid wall shelf mounted to the studs of a load bearing wall