rca is the cable that you connect between the head unit and the amp.. its like the video audio cable on your dvd player.
you need to swap it around and see if you still get the same issue. if you do get the same issue then its in the amp if you get the issue other way around then it can be the connection between the head unit and the amp which is the rca,
it can be loose or not connected at all at the back of your head unit
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