Default CS918 temporary blackout issue

I have had a CS918 box for around 4 months and it largely works very well, however every now and then (once an hour maybe, sometimes two or three times in the space of a minute though) the screen goes blank for a second or so, the sound also cuts out for this period of time also.

I was using stock firmware, recently updated to a 1080p kernel and custom rom, but this still persists.
I've changed the HDMI cable and the slot it's in also.

I'm leaning towards a dodgy power supply - has anyone else had this issue?

Many thanks