Reply to Ecler NUO.3 + Traktor scratch pro issues.

Hi. I need a hand with a little problem I have.I connect my traktor to the high line-in of my nuo3. And when starts the reproduction you can hear a cracking / popping noise that really can damage the speakers (is that loud...). Only happens in 1 of the channels and already I believe I have localized the problem in the gain mixer. Any idea if is only dust or else easy to fix or needs some part replacement?
Thanks in advance for any help you can give me.