I think that one company is called Shepherd. It's whatever company Salamander Designs racks uses, for their large locking casters they offer under their cabinets. I tracked down that company, and you can buy different versions that have flat plates that can be screwed to the bottoms of just about anything. And they were way cheaper than ordering through Salamander. They can handle a lot of weight, and have rubberized non-marking 'circles' that make contact with the floor. I seriously doubt you would notice much of any sound degradation, in fact it might actually be an improvement.