I was wondering if someone can help me locate a problem. I bought this MM100.4 that channels were going in and out and the company I was dealing with sent me another one but its having the same problems. Except with this one the amps channels all work but sometimes depending on how im drving the speakers will crackle like the input signal is going in and out. The amp that they sent me also was missing a screw to hold to the RCA jacks to the amp casing and the RCA jacks where kinda pushed inside the amp. I put a screw in to hold it temporarly but its not the right size screw to fit it. What could be causing the speakers to crackle????