Why? Is the wife's TV bothering you? (j/k)
There are a variety of ways, varying in cost and complexity. A double layer of drywall helps, and they make deadening materials to sandwich in between. Another scheme is to 'de-couple' the wall, building an isolated second wall. Probably too late now, but this is often done with staggered studs, with the house drywall attached to one set, and the garage drywall attached to the other. A typical wall acts like a drum, transmitting vibration through the studs from one side to the other.