The least expensive option is going to be to create white noise.
Otherwise, you'll need some type of sound insulation and dense pack cellulose might be able to be retrofitted into the wall cavity. But ... read more
If an ordinary residential unit won't work for you, then you should consider something such as a Santa Fe, Ultra Aire, or another unit made by Therma-Stor. These are the kind that can be ducted, have ... read more