Bob Reynolds wrote: "It may be that the Peachtree product's filter doesn't attenuate enough for high sensitivity speakers."
By definition, ultrasonic noise in an amp does not create audible hiss - its beyond the range of hearing. At worse, if unfiltered, it is going to create an intermodulation problem in the audio band, but that only exists when music (an audible signal) is being played. In that case, you will not hear hiss, but rather some type of distortion in the music.