SVS - SoundPath Subwoofer Isolation System (Set of 4) - Music Direct
Auralex SubDude II Subwoofer Isolation Pad | Sweetwater
Aluminium Subwoofer Isolation Stand | Metal Subwoofer Isolation Stand - Audio 4pcs - Aliexpress
SVS Subwoofer Isolation feet compared to standard feet. Looked promising, but made little to no difference in rattling on mantle/walls/etc. : r/hometheater