Subwoofer rumble issue


I’m having a hard time solving a problem that seems to come and go. My subwoofer will rumble uncontrollably when playing records at a higher volume. If I turn the volume down sharply it goes away but when I creep the volume back up it comes back. I’ve tried isolating my turntable as much as possible with diy books, isolation feet, etc. (I don’t want to buy an expensive isolation platform unless that really is the issue.) Any thoughts on what I can do to fix this? Thx!
paulgardner
Just did a quick test just for fun and placed a pillow under my turntable and the rumble is gone! Super tight bass! So maybe it’s not actually airborne?? Just need some extreme isolation? Hmmmmm interesting 
Almost certainly one or two of the 12au7's will be the pre stage output tubes.

Cheers George
what I notice on this topic is that when listening to recordings posted on youtube if the track is from vinyl you can often tell as there is obvious woofer pumping, I assumed wrongly that a signel might have been high passed to get rid of some very low frequency hash, apparently not. Many dance/electronic 12 inches not available on digital format have been uploaded and show this.
I’m having the same problem. I have a Technics 1200 M3D and KEF LS50s. No issues. I just added a REL T7i and have the runaway feedback rumble at high volume. I added Isonoe footers to the table which didn’t do much. Unfortunately the table and speakers sit on a big media cabinet from Design Within Reach which is not ideal.  Not sure what the right next move is.  More table isolation, put footers under the cabinet legs, new turntable, new furniture, or new house?