Have a protein skimmer or other equipment inside your stand that’s creating a lot of noise? A good solution to this is to use sound deadening material like foam or even the material used in the car audio industry. Line your stand’s doors, walls, and ceiling with the material if possible. This won’t fix all of the noise issues, but it might reduce the volume of the annoying sounds enough to where it’s not longer a problem. Be careful with the foam though, as it can also cut down on air circulation within the stand and cause heat issues that could increase evaporative rates or even the operating temperature of the aquarium.