Sound problems after using for a few hours?

After using my CDJ's for a couple of hours one of the decks starts to play all of the tunes with a throbbing like echo. There had been no problems at all then all of a sudden this starts to happen. I have tried turning the unit on and off and selecting other tunes on the USB but it appears to happen on all of the tunes it plays?

Any ideas why the deck would start doing this?