Hello OP,
Granite is both reflective and absorbent depending on the material science and finish. The frequency of the shelves vibrating adds to the overall sonic in the environment. It creates additional noise elements or rack chatter. This effect also transfers into the electronics package, producing inefficient component operational performance and affecting their sonic.
I recommend placing a resonance conductive metal or alloy material on top of the granite shelving below the component. Thickness is relative to material selection. This addition will reduce the sonic signature and frequencies of the shelving while establishing a rapid sink for resonance flow.
The material selection is critical due to natural damping factors related to the materials.
Rubber and cork dull the sonic in components via absorption.
Springs suffer from spring fatigue. A small amount of fatigue delivers an audible loss in the leading edge dynamics. They are affected by weight, and the design wears out and should be replaced with new springs routinely.
Decoupling defies the laws of gravity and is a word established by the Audio Industry to sell more products.
I recommend adding component footers after the rack function has improved and installing versions that match the overall design methodology.
We are willing to assist with overhauling the design without charge should you want to turn the granite rack into a performance-driven platform.
Feel free to contact me.
Robert
LiveVibe Audio