Vibration and Isolation at a budget?

I am looking into isolation products as well.

Sorry if I am highjacking this thread.....

I have a Blue Circle BC27 phono stage for audition now and if I raise the volume high enough, there is this very low frequency energy being reproduced by the speakers.
My Pro-Ject Tube Box MkII phono stage does not do this either with rumble filter on or off.
I suspect few things as being the cause of the problem:
1) The problem is feedback and not really a turntable rumble per say;
2)the table isolation;
3)BC27 stage reproduces these lower frequencies and Pro-Ject attenuates them.

I have my table simply on the top shelf of a Salamander Archetype 2 and there is nothing in between the shelf and the table. Table, a Pro-Ject Xperience, has stock cone feet.

Am I correct in my assesment of the problem?
How can this be cured?
If the isolation is the cause, would a Mapleshade platform with isoblocks be more or less effective than, say, Ginko Cloud 11?
Thanks!

Also, interesting, I've noticed, by searching the forums, that some use bubble wrap under the isolation platforms. This is kind of cool to exepriment with, as at least the bubble wrap costs nothing.

Tvad, I just scored a Pro-Ject GroundIt Deluxe platform at a pretty increadible deal! I am psyched to try it. It is still sealed in the box. I just picked it up. I may be interested in sorbotane. Supposedly the platform has coned feet, but I am pretty sure they're removable. I'll e-mail you as soon as I get to open the box and inspect what it is. Thanks man!