Using Ldubs' idea as an inspiration, I used thick felt stick on pads intended for use as furniture feet so they don't scratch wood floors. Worked perfectly.

Two where the screws attach the plate, two in the middle of the plate, evenly spaced, and a double layer on each of the bottom corners. Not a peep from the plate even at extreme volume. And you cant even tell they are there.

Riff, I have a practical suggestion for you. Remove your keyboard.