Xdj rx drifting slightly

Hey guys 

Do any of you have any issues with the rx drifting slightly off beat every now and again? I find that random tracks seem to go off just a bit(nothing major) but it's enough to get your attention so to speak.All my tracks are purchased from various sources and have checked the beat grids and all seems fine.Just wondered if it's a firmware issue and if pioneer are aware of this.