Strange turntable/speaker issue

I have a feeling someone else has experienced this, and want to get some advice in how to correct this issue.

Some background; I could not keep myself from wondering just how good the old vinyl I had boxed up for years would sound compared to my digital set-up, which sounds pretty good to me right now. But, out of curiosity, I finally dragged up my old turntable that has been stored in my basement for 15 years (since I moved in), and probably have not used it in at least 25-30 years total. Originally purchased in the mid 70’s, it is a basic Kenwood KD-2055 with the heavy composite ‘granite’ base. After getting it set-up, I realized very quickly the old Ortofon OM 5E cartridge I installed in the mid-80’s was not going to ‘cut it’, and could not compete with my CD’s, files, or streaming set-up. So, after doing a bit of research, and not knowing yet if going back to some vinyl listening would stick, I purchased a Grado Premier Red, mounted it in the shell, set it up, and yes, it is a vast improvement. Much better overall dynamic range, soundstage, imaging, etc. than the Ortofon 5E. I thought to myself, ‘this may just work’. But, as I was checking some things out, I realized my Vandersteen 2CE’s were actually moving quite a bit (volume was a bit high, but not overly so). That is no easy task. I got back behind the Vandy’s and the rear 10” acoustic coupler was actually moving in and out at a fairly rapid speed, thus causing the speakers to actually move on the anchor stands quite noticeably. Now, this was not really effecting the sound, or creating sound in and of itself, but it can’t be good. First thing I thought was I had misconnected the cartridge leads at the shell, so double checked, and they are connected as per the Grado instructions. BTW, this could have been happening with the old Ortofon as well, but I may not have noticed. Overall, while playing music, the turntable also seems highly sensitive to moving/walking around as the music was playing without distortion. I don’t have to tell you, this does not happen with CD’s or digital files.

I have my turntable on top of a pretty beefy steel frame with wood shelves 60” long ‘TV stand’, as yes, my system also acts as a ‘home theater’ setup, as well as a 2 channel set-up for music. The Vandy 2CE’s are my ‘front’ and 2 channel speakers driven separately by a B&K 125.2 power amp. The lowest shelf of this unit consists of CD storage, the middle shelf my B&K amp, Yamaha V871 receiver (I use as my pre in 2 channel, although it does little as the front channel pre-out’s go directly to the B&K, and while playing music I run in ‘pure direct’), CD player, and PS Audio DAC which all my CD’s, files, and streaming runs through. The top shelf is my TV, Elac center speaker, and my turntable. At this time I am using the Yamaha phono stage (that could change soon, as I think a dedicated phono pre-amp would help things a lot). The TV/equipment stand sits directly to the side of the right speaker, not between the Vandy’s, as they are on each side of my fireplace. The turntable is about 4 1/2’ from the right speaker, and right about the same level of the Vandy’s front 8” woofer.

So, all that said, I have a feeling what I am getting is sonic feedback between the speaker and turntable, perhaps with the cartridge acting as a microphone getting hit with the sound waves from the right speaker, even with the dust cover down. Because of room and layout constraints, I have very limited locations for all this stuff, so not sure a relocation of the turntable is really possible, and if I did, would have to get long male/female RCA interconnect extensions to get back to my Yamaha, or any future phono pre-amp, which would still have to run back to the Yamaha probably utilizing the analog Audio 2 inputs, as the Audio 1 inputs are serving the PS Audio DAC.

So, is sonic feedback what I am witnessing? Or could it be something else? And is there any easy solution? I doubt isolation feet will solve anything if feedback between the right speaker and turntable is the problem.