RCA audio output 900 nexus

Hello,

When I plug one of the two CDJ 900 Nexus into any track on my DJM 800 via the RCA audio output, the cue sound crackles slightly in the low frequencies.

I have no problem with my second deck. I've tried changing the cables and swapping the inputs on my deck, but nothing works. The cue sound on my first deck is much less clear than on my second deck, no matter where I plug them in. The low and middle frequencies crackle, but the highs are fine... Yet my headphones are new (HDJ-X10)...

Could this be coming from the RCA audio output on my 900 Nexus? Is it the sound card? Is it the circuit board on my RCA connectors?

Thank you very much for your help!