That's a nice table, but lightweight suspensionless tables like that call for a good solid stable and isolated shelf to get their best. What you are seeing is micro vibrations you can neither see nor feel but amplified 8000 times are enough to make the woofers pump back and forth like that. Way too low in frequency for you to hear it, and it doesn't really hurt anything either. But if it drives you to put the table on a more isolated shelf that will definitely improve sound quality and make it a two-fer and well worth doing.
The budget solution is to put the Rega on a thick solid shelf of something like butcher block or thick MDF. Then use Nobsound springs under that. This will just about eliminate the woofer pumping while improving sound quality a lot.
The more expensive but by far superior solution is use a similar shelf but with Townshend Pods instead of Nobsound. Pods will remove a layer of harmonic resonance you never even knew was there, until it is gone. Instruments take on a much more realistic natural timbre. Bass and midrange become a lot more clear, the top end a lot more liquid. For a table as good as yours, if you can afford Pods, that is totally the way to go.
The budget solution is to put the Rega on a thick solid shelf of something like butcher block or thick MDF. Then use Nobsound springs under that. This will just about eliminate the woofer pumping while improving sound quality a lot.
The more expensive but by far superior solution is use a similar shelf but with Townshend Pods instead of Nobsound. Pods will remove a layer of harmonic resonance you never even knew was there, until it is gone. Instruments take on a much more realistic natural timbre. Bass and midrange become a lot more clear, the top end a lot more liquid. For a table as good as yours, if you can afford Pods, that is totally the way to go.