Reply to S4 has loud buzzing and clicking noise in headphones only

I am wondering if anyone has this problem - in the right cue side only I sometimes have a buzzing sound that occurs when I load a track and press play. Then if I press play again and cue it stops. Also, when the track is playing there is a clicking sound that almost coincides with the beat of the song. Remember - these sounds are only heard in the headphones. The live output heard by the audience is clean. I have tried recalibrating the decks, but it does not fix the problem. Any help would be much appreciated. Thanks!