Granit amp stands are they killing my sound?

I use a 2" thick concrete patio slab 20" square (cost $3). Up on tiptoes (old stock have had for ?25 YEARS. $28 when new) , with the amp on size ten butyl rubber bottle stoppers on top of the slab.(another $6)
Cheap as can be and works great.

Granite may 'ring' a tiny bit, but it may not, depending on how the amp sits on it. Personally I have never been able to hear a chunk of granite make any sound, or feel it vibrate in any way.

PS if you have to ask this: guess what: IT DOES NOT MATTER because you don't hear any difference anyway.
IF YOU did hear a difference, then you would not be asking...
You are worried about the granite 'in theory' WHY???????
Do you just worry about useless stuff? And guess what.. asking here will get you a dozen different 'theories' right back, Not ONE of them is worth a damn. as they are all just 'theories' too! They can't 'hear' your amp on it's granite stand, only YOU can. Rant over.
(Sometimes it IS neccessary to kick butt...LOL)
And I apologize if the op feels hurt by my rant...

And if the granite ringing in theory bothers you, add a constrained layer of damping material to the bottom of the granite.
A dirt cheap version would be a self stick vinyl flooring tile. just stick on the bottom. problem solved. in 'theory anyway.

Depends how thick the granite is. I use three inch thick granite at are lake system without issue.
Solid state amps aren't generally susceptible to the things there put on.

I have tried many different materials under my amps, preamps, cd players and turntables. My 3" granite slab is among the worst sounding of them all, no matter what type of couplers or damping materials are used. I don't believe the problem is as simple as "ringing" because it's hard to believe a 180lb slab of anything is ringing. But the granite does have serious colorations and they are unmusical colorations---they interfere with my enjoying the music.

I recommend trying some different types of wood instead of the granite. Each type sounds different and different thicknesses of the same wood sound different. You just have to try some yourself and reach your own conclusion about what you like best. My bet, however, is that the wood will sound much better than the granite.

A safe recommendation is to use a shelf platform made of 3/4" Baltic Birch void-free plywood. I have found this to be very neutral tonally with good dynamics and detail. Don't be tempted to use 1" Baltic Birch (too dull in the treble) or some type of plywood other than Baltic Birch. And whatever you do, stay away from mdf. Despite lots of companies using it for equipment shelves and speaker cabinets, mdf is also among the worst sounding materials.

Wood might work, but pay special attention to grain orientation, which can be easily heard. Its far worse than ringing. Wood is even more directional than a fuse, and you wont want a grainy sound.

My, my. We have so many 'material scientist' on the forum, all doing in lab experimentations. Great, especially the wood grain orientation from Mike60. Me, I use some steering wheel covers I got at Target for $4 each. Works wonders. So why do we see so many glass equipment stands?