Subwoofer rumble issue

Thanks for all the reply’s and ideas, awesome! I’m running a Clear Audio Concept table and the sub is a REL T9i. They’re both very good products so the lack of quality materials in the turntable build is likely not the issue. I will do the stylus down on a still record/finger tap on platter test later today and report back on the weather conditions - earthquake or other! I’m not sure how I feel about a subsonic filter. Maybe as a last resort but moving the table to another room is not really an option - I live in a 2 bedroom condo loft with 20 foot ceilings so it’s essentially one big open space with 8 foot half walls for bedrooms and a bathroom and furnace/washroom being the only closed off rooms. I will report back on my findings! 

I had the same problem after moving my table from a sand-filled platform to a new wife friendly cabinet. 

A Ginko cloud platform solved it for me.

I should add all (rpt all) components including front end electronics should be isolated. Not only because of subwoofer mechanical feedback but also structure borne vibration. It’s a vicious cycle.🔄

Paul, two possibilities. If your sub has room control turn it off and see if the problem goes away. Then as others have mentioned, feedback which can be worsened further with room control. The feed back can be due to a cartridge tonearm mismatch but can also be due to improper turntable isolation.  An SME , SOTA or Basis turntable will never do this.

Paul, I forgot to mention. Get a Hi Fi News Test Record to check where your tonearm/cartridge resonance frequency is.

Mike