From what you say, sounds like your unit is screwed up. I once bought a highly touted Tascam dual track tape deck; that sucker made noise every time I pushed a button--ANY FRICKING BUTTON. I concluded that the soldering and/or transisters were from the Klingon empire and I gave the unit to one of my nephews. Every punch of a button screwed up whatever I was doing with "aDDED sounds," the kind of sounds that you do not want.
Other than a defective unit, all I can is that you have your unit hooked up in a manner that screws up its performance, and that is probably highly unlikely but still possible.