spring loaded platform non-suspended turntable

Fingerpaws...oh yes you do have acoustic feedback...its just not at a frequency that you can call it that..however, it is blurring the sound coming from your turntable. Your fix (given the springy floor), is to mount a shelf on the wall for your Classic - affix it to studs. ( had one of those VPI spring things too). Get it off of that.... Get Bearpaws to replace your mini feet, and be delighted at how much more clear sound you get...more definition, more bass, clean, clean, clean.

Stringreen, I respect your musical knowledge and experience, but I believe you are wrong about "acoustic feedback". My simple understanding is that it is the airborne (i.e. acoustic) waves from output back to input. The most common example most of us have heard is an improperly set up microphone in a auditorium which howls from the sonic loop from PA speaker back to the mic.

Similarly, a turntable/arm/cartridge system is subject to the sonic energy, particularly low frequency tones, from the speakers. Wall mounting will only be effective if it moves the tt system away from a bass node loading area. It is not related to a springy floor. In extreme cases I've seen the tt system placed in a separate room from the speakers to minimize acoustic feedback. Fortunately most of us don't need to go that far.

This is why I suggested consideration of all three conditions for unwanted energy in my post above.

Or, you can place ten cryo'ed Baby Promethean Mini-Isolator Springs (from Machina Dynamica) beneath the solid base of a 100 pound turntable.
Or, a higher number of these special springs if the total weight is higher due to the weight of any supporting solid base already currently beneath the turntable base.

This is quick, low cost, and easy to level turntable.

Due to limitation of my own personal lifting strength, I have not positioned a turntable/base heavier than 50 pounds where I happened to need only five of the Baby Promethean springs to properly match the 50 pound load to be supported.

Vinyl reproduction capability is beautifully enabled.

I highly recommend Minus K for non suspended turntable. I used to have my TW Acustic Raven AC-1 on Symposium Ultra sitting on top of machine shop bench which has 4 inch granite table top with steel legs. The whole thing weigh about 100+ kg without the turntable. Replacing Symposium Ultra with Minus K was remarkable and in my opinion, well worth the difference in price of the two platform. I don't have problem with subsonic rumble or acoustic feedback through the floor but sonic benefit alone is quite impressive. I also heard VPI Classic 3 to good effect on Minus K. There is even a review of Minus K on suspended table like Linn floating somewhere in the internet and there is a recent review of Minus K on Positive Feedback wiht some comments regarding Minus K vs older version of Vibraplane as well.

Pryso....I suspect that you are right, but remember too that sound travels as well through springy floors (and walls)...low tones travel unimpeded through windows (listen to the delivery trucks going by), but the glass is reflective of the higher frequencies....(cover all windows and/or close the draperies to hear the difference in the room. My suggestion of mounting a turntable on a shelf mounted securely into the wall studs eliminate a surprising amount of vibration transmitted via springy wooden floors...no its not perfect, but I have frequently been surprised at how much better the performance of turntables on walls is improved. Certainly this is only a suggestion and you are encouraged to do as you see fit...but if you try my suggestion, it very well might surprise you too. My recommendation of Bearpaws to replace the mini feet still apply.