One more thing!!

Can a Turntable Dust Cover Cause Acoustic Feedback?

On a well‑isolated turntable, the dust cover generally does not cause acoustic feedback. Its main purpose is protection, and in a stable setup, removing it usually makes no noticeable difference in sound quality  .

However, on a less stable setup, the dust cover can act as a resonator or vibration path. If the lid is thin, hinged, or placed on a lightweight or resonant surface, it can pick up vibrations from the table, speakers, or nearby objects. In such cases, the cover can amplify or transmit vibrations that might be perceived as feedback or unwanted noise 

That’s a good point @yogiboy the dust cover can definitely contribute 

Just speculating based upon the picture of your room -- it could be the combination of where you placed the turntable, the dust cover and/or cartridge/tonearm setup.

At this point you don't need an audiophile type equipment rack, but you do need to make sure the furniture the turntable is sitting on is stable and preferably has some mass to it.  You may have placed the turntable in a spot that reinforces bass energy which is then fed back into the turntable by the dust cover and/or cartridge tonearm.

I would start by taking off the dust cover and see what happens.  If the problem still persists then reinstall your cartridge.  Make sure the resonance is within the proper range.  Finally move the turntable to a different location.

Try what I have suggested before spending money on isolation devices and equipment racks.  They might solve the issue.

Question -- does the Technics tonearm have dampening?

I had the same problem years ago using a DD deck on an unstable stand on a suspended floor. Switched to a belt drive and the issue stopped.

I am currently using a lesser Technics DD deck (SLQ2) and a shimmed, for VTA, AT 440 MLA cartridge on a concrete floor. I never leave the dustcover on during play. No pumping from Velodyne sub or from 6.5” midbass drivers. Also using entry level NAD pp2e phono pre.

Remove dust cover, place the player on isoacoustics zazen 2 or equivalent. That's what I did