It might be your turntable. I had a Concept and it was super sensitive to footfalls. I couldn't walk anywhere near it without the arm jumping around. Granted, I have springy floors and it wasn't very well isolated, but I've had a number of tables before and after it that didn't have that problem. I seem to remember issues with what you've described at high volumes also.
It's surprising and unfortunate, because it does seem to be a solid and well built table. It may have something to do with the magnetic bearing tonearm design.
There are a number of reports of this issue if you do a web search. There are also many who love it and report no problems with it. There seems to be a consensus that it needs to be really well isolated.
I really liked mine and wanted to love it, but it didn't work in my less than ideal setup where many other tables have worked great. You'll notice I use the word "seems to" a lot in my post, there's obviously some supposition on my part, as I was never able to figure out how to get mine to work satisfactorily in my system and I know many others have that table and love it. Do you have another table you can try out and see if it has the same issue?
