Subwoofer rumble issue

First look to see how much subsonic turntable rumble is getting through. If the woofers flutter a lot at high volume even with no signal, like on the lead-in and lead-out grooves, or between tracks, that’s one thing.

Also does this ever happen playing CDs?

If you have no problem playing CDs, and especially if you also have a lot of flutter, then yes you need a better platform.

Just not any sort of isolation platform. There is by the way no such thing. What there is is vibration control. This false notion of isolation makes people forget what is so plainly evident, that a box full of sand ain’t gonna isolate nuttin but it certainly will control and eliminate a lot of troublesome vibrations reaching your turntable.

I hear ya on the isolation thing. It does rumble in between tracks. I do not run a CD player, just phono. I’ll keep playing with trying to reduce vibration. Hmmmm

Perhaps you have too much gain going to your sub or you have it crossover too high. Let us know if you find a solution. All the best