Sound Dampening Material

[RaymondL]

I'm wondering if anyone has any suggestion for a sound proofing/dampening material that I can use on an aquarium stand. There is a hollow wooden cavity 'shelf' that is directly under that wooden top that the aquarium sits - I believe this is amplifying the vibration sound from the aquarium up top. In this cavity - shelf, I can really hear the vibration sounds from the aquarium.

Thanks

 

[Bridgerdean]

Spray foam from Home Depot.

 

[Idech]

Old yoga mat