Thanks for the help. I tracked down the problem. It turns out that the cable going from Mix3 on the QU to the DVD recorder was not wired properly. The RCA is spliced to the microphone wire, and it was not spliced correctly. The ground/shield wire from Mix3 was spliced to the two black wires on the RCA, which is correct, but the red and black wires from the XLR were spliced together with the two red wires from the RCA. Basically, the red and black wires were being crossed in the splice and that must have been what was causing the crackling. I’m not sure who wired it that way, or why, but it definitely was not right. Thankfully, it was an easy fix!
