For my Sound Organisation rack with glass shelves I used two strips of 1" x 8" Black Hole Pad adhesive dampening material on the surface of the glass beneath each shelf. This helps to dampen any ringing.
If the glass sits on a supporting frame the use of a relatively soft supporting material can also help. Herbie's Audio Lab Grungebuster Dots would be a good choice for this application.
The Tenderfeet recommended is a good choice to interface between the equipment and glass shelf. I've had very good results with these and the Iso-Cups and balls noted above. The Supersonic Stabilizers are usually used for chassis vibration. I don't have enough experience with them to make a firm recommendation but they may be helpful to you.
I'd give Steve's recommendations a try. Fortunately Herbie's Audio Lab has a 90-day Trial Period on all products for full refund or exchange for a different product so you'll will not be stuck with something that does not provide a satisfying solution.