pioneer ddj rb rekordbox, audio crackling issue after 15-20 mins playing

having major issus with the ddj rb and rekordbox, crackling audio after 15-20 mins on using the rb sound option, tried upping slider for buffer, doesnt change anything , tried updating firmware of controller no effect, 

is there anything else it could be before i return this machine to the shop i got it from ,

could it be soundcard problem i need help pioneer not impressed as is stands !!

i have come from using m audi tech equipment to which ive had no issues 

help help help help help help pleaseeee