Platinum Silicone Hemisphere Bumper, Non - Skid Isolation Feet with Ad – Hudson Hi-Fi
EveryMarket
SVS - SoundPath Subwoofer Isolation System (Set of 4) - Music Direct
SVS Subwoofer Isolation feet compared to standard feet. Looked promising, but made little to no difference in rattling on mantle/walls/etc. : r/hometheater