Thanks SoCalRacer. I had previously read that article, but thanks for pointing it out.
I was really after some real world experiences from others, in that the 3 seconds up/down cycling would rule some of those devices in the list (microwaves, cordless phones etc)
I think I'll need to visit again and try and zone in on the problem. It is seen strongly by 3 of the 8 AP's (I had set all 8 to ch1 and checked in RF spectrum in the dashboard), so it looks isolated to a particular area, hopefully that will help
Thanks