Abstract: An improved soundproofing system for a window sash mounted for sliding vertical movement between jambs of a window case includes first and second jamb liners which are mounted on opposite jambs of a window case, and which each define a vertically extending channel in which a coil spring is disposed with one end connected to the window case and with an opposite end connected to a sash which is vertically slidable between the jambs. At least one strip of sound-absorbent material such as felt is wrapped at least partially around and attached to each of the coil springs. Each of the vertically extending channels includes an open side which faces away from the jamb. A spring cover is connected to and closes a vertically extending portion of the open side of each of the vertically extending channels. The fabric strip wrapped around the springs, and the spring cover, together or separately substantially reduce objectionable noises generated by the springs.