CDJ 2000 NXS 2: Volume Dipping/usb ejecting

Hello!
I hope some one can help!

NXS 2 reads usb and works as it should. After a playing a track or two the the volume of the track that is playing dips, it some times comes back or the usb ejects - no error code comes up. This obviously makes the CDJ unusable.

The CDJ has got the current firmware updated and has been reset. We've used multiple usb's and we are fairly certain its an issue with the cdj and not any formatting issues with usb etc

Ive got the usb port replaced and this issue is still there. My thoughts at the moment is the eject button may be having some issues as the music dips - like it would if you eject a usb on a CDJ that is playing.

Has anyone else had this issue before?

Any advice would be hugely appreciated.