Left side of line 1 destortion!

PLEASEEEE HELPPPPPPP!!!!!!!

So im having problems with the left side of my line 1... I've trouble shooted everything and really cant figure out what it can be!! The problem is intermittent! When it happens the sound sounds destorted. It happened to me this past saturday at a gig I had and its happened to me before that too! When it first happened to me, I ended up buying a new serato box and it was fine until this saturday evening ! , so that rules out the serato box! While it was happening I switched the line 1 connection on the mixer to line 2 and it sounded fine so that also rules out the box and laptop! I took the line one connection from my serato box and switched it to line 2 and it sounded fine, so that rules out the mixer and RCA cable. I also switched the USB cable to the other port and also changed usb cable and it does the same thing, so its not any of the ports on my mac. I played a cd on my cdj and connected it directly on line one on my mixer and it sounded fine!!!!! THIS IS DRIVING ME INSANE AND NEED TO FIGURE OUT WHAT IT IS ASAP!!!!!!!!!!!!!!! I HAVE A BIG EVENT THIS SATURDAY!! CANT TAKE A RISK!!