Tonearm microphonics

Thank you all for your continued input; it's very informative. 

It appears then that a happy medium is key...??

I'm glad this subject was broached.  I've been in contact, just this week, with two well known experts in the hi-fi field, concerning acoustical feedback in my TT, when playing low frequency LP's at a louder than normal level.  The bass begins to build on itself and in a few seconds, I have a low frequency feedback problem.  In reading this thread, I noticed it was mentioned, one should never get any sound, when tapping on the TT plinth.  I have a VPI Scoutmaster, with a JMW-9 signature tonearm.  The cart is a Dynavector DRT XV-1s.  With the tonearm at the end of the record, I can tap on the plinth with my finger and clearly hear the thumping noise through my speakers.  I have tried a couple of methods to dampen the tonearm (haven't tried the shell yet-there really isn't one) to no avail.  I'm thinking this has to be contributing to my problem.  I have also tried dampening the plinth by placing sealed bags of sand on top of it any trying the same test.  The tapping noise is still there and has not been diminished in any way.  I wanted to employ a subsonic filter that would eliminate all frequencies below 10-15 hz on my subwoofers, as when they're turned off, the problem goes away, but can't find one.  I'd rather not go the KAB way as I think I would be losing some of my good frequency response.  I realize most of my problem, must be coming from my tonearm, but was curious about the plinth comment.  Does anyone have words of wisdom for me about my tonearm and plinth?  BTW, I've tried rearranging my subs and have significant room treatment.  My room is not just an untreated shell.  

@handymann A year ago or so, I had the same problem as you, especially with LOMC cartridges.  The solution was isolating the turntable.  In my case, I used Anvil turntables excellent magnetic footers, but I'm sure there are other good solutions.  These isolating footers works despite the fact that my table was in the front corner next to the speaker with a powered sub.  Ultimately, further improvements to the sound of my system occurred when I moved the turntable out of the front corner to the rear of the room using a long XLR connection between amp and preamp.

FWIW, I tried the tap test on my Koetsu/FR-64S combo this am, with the pre at playback volume.  I heard nothing through the speakers.  Admittedly, I didn't have someone's ear right in front of the speaker.

Karl:
When trying the tapping test, be sure your stylus is on the album at the end of it, where it tracks out.  If at rest or cued up, you shouldn't hear anything.  I use all balanced interconnects, except from my turntables.  I have to use SE there

BTW, I have one TT on an inner tube and spiked, the VPI is spiked (it comes with it's own adjustable spiked feet) onto the discs that come with spikes.  The spike discs are on rubber compressor feet and my TT platform is isolated from the wall.  I don't think it's an isolation problem.  I can tap on my platform, when the record is tracking out and I hear nothing through my speakers-standing at my TT position.  Thanks for the input-always wanting to learn.