Pioneer DJM 750 MK2 DVS/Faulty Phono Inputs

Hi, Wondering if anyone can help me out. I purchased a Pioneer DJM 750mk2 around 6 months ago. I have used my mixer purely for bedroom use and i have never had any issues up until now. I'm running rekordbox dvs through my mixers interface and recently when I try use Dvs one of my turntables (left deck) just make a scratching sound when I try play a track through rekordbox. I checked all my settings in rekordbox and they are all correct. All my inputs are into phono. For some straight reason channels 1,2 and 3 are giving me the same problem but 4 is working fine. I changed turntables because i thought maybe the phono leads on the back were faulty but that wasn't the problem. I was really confused so I played a normal vinyl record through channels 1,2 and 3 and for some reason only my left monitor works. I've updated my firmware to the latest version and still having issues??