Sub frequency issues with vinyl

[Confused]

I read "Devialets" to mean Phantoms...hence most likely the OP is describing acoustic feedback?

Ah yes, it looks like you are right.  I should have read the question more carefully, my brain is wired for Expert.

So this then begs the question, what is the OP using as the phono stage, and does this have any kind of low frequency (sub 20Hz) filter option?

As an aside, the Phantoms inherent latency should actually be advantageous in terms of avoiding acoustic feedback, but this is only part of the problem, turntables are incredibly sensitive.  Without a low frequency filter, I can walk towards my turntable and see the woofers responding, and this is with a solid concrete floor.

Thanks everyone. Using a Musical Fidelity MX-VYNL Phono stage and a RME ADI-2 Pro as the analogue to digital converter. Any ideas ? and yes playing 2 Devialet Gold's

From what I can see on the 'net, the Musical Fidelity MX-VYNL has selectable equalization curves, either RIAA or IEC.  The "IEC" curve is the same as the "RIAA 1976" curve that I mentioned earlier.  So in theory, by selecting IEC you should remove the majority of the pulsing movement that you are experiencing.  I say the majority, because the IEC (RIAA 1976) curve does not eliminate the lowest bass, it just invokes a steeper roll off for the frequencies below 20Hz.  Above 20Hz, the curves are very near to being identical.

From your description in the original post, I have to assume the phono stage was set to RIAA, so try the IEC setting and see how you get on.  If you still have issues with the IEC equalization curve, then you only remaining option will be to look at improving the turntable support and isolation.