Just wrote an impressive rant about mechanical isolation, but had second thoughts about posting & deleted it... didn't want to offend anyone who's spent lots of money on "magic racks"...

The chances of these products having an effect in an acoustically, mechanically and electrically quiet room is teeny tiny.
So if they have an effect that's noticeable, the room must be buzzing/humming/shaking to a degree that is noticeable by its reduction.
Far better to decouple the room, use earthed foil backed sound proofing as insulation etc. I've seen installs where the cost of the build technically exceeded the components (figuring in labour) because they were done correctly. I've also seen ripoff jobs where someone blew �250k on kit that will never sound good no matter how much snake oil is applied.