sound crashing / slow playback

Hi,

I'm using a DDJ-RR Rekordbox (all firmware and drivers up to date).

When i'm playing tracks everything starts off fine then randomly the sound crashes into a high pitched interference (almost mosquito or dial up modem) and slows right down.
I can vaguely hear the track in the background.
In the build up to this crash there are intermittent 'clicks' in the sound quality too.

I'm pretty sure it only happens mid mix although I could be wrong.

I've checked the laptop resources and at no point are any of the parameters (CPU, RAM etc) under any strain.

I've increased the buffer size to max and this makes no difference.
I've also tried purchasing a dual usb 'Y' cord to make sure the link between controller and laptop are sufficient.

Please help !!