Sub Sonics and woofer pumping

Its probably the rack. Different approaches can be taken. Here's mine:https://systems.audiogon.com/systems/8367
A good relatively simple way to see if this is indeed the problem is to set your turntable up on the floor. The best rack is no rack and the floor is pretty hard to beat. If the floor is indeed better then we know its the rack. The next step is either a better rack, or use something like a shelf with mass like sand, or springs, or something to help reduce rack vibrations from reaching the turntable.

Yeah. Maybe. The thing is sound isn’t up loud enough to cause vibration In the turntable. 

Are you saying the operation of the TT is causing the pumping?

Here's a good explanation -

https://www.audioadvice.com/videos-reviews/why-does-my-turntable-make-a-loud-feedback-sound-when-i-turn-up-the-volume/#:~:text=The%20cantilever%20on%20the%20end,what%20creates%20the%20feedback%20loop.&text=The%20bad%20news%20is%2C%20even,muddier%20than%20it%20should%20be.

Never said one word about feedback. Gave you the steps to figure it out. Try it on the floor. Good luck.

Last lemming, you have several problems culminating in amplification of rumble. The most significant one is that you are using a very stiff cartridge in a uni pivot arm. Your resonance frequency is too high and you are amplifying rumble inherent in records. You will need to add mass to the head shell. In order to determine how much you will need a test record with resonance tracks like the Hi Fi News Analog Test LP. You want to get that resonance frequency down below 10 Hz. Uni pivot arms are a problem because they have a third degree of freedom and a third resonance point, the rotary one. The best way to avoid issues with rotary resonance is to use a compliant cartridge like an Ortofon 2M series cartridge. They run around 20 X 10-6 cm/dyne. The Nagaoka is 8.5 X 10-6 cm/dyne. It is a great cartridge but it was designed for a heavy gimbal arm. I think you can get the rumble down to acceptable levels by tuning the system. If you can't then there are only three solutions, change the cartridge, change the tonearm, get a rumble filter. My preference would be a new arm. The Nagaoka will work perfectly in an Ortofon arm and they are relatively inexpensive. Soundsmith sells a dandy set of graduated head shell screws. Put the heaviest (Stainless) screws on and tell us what happens!