Just ordered a pack of ferrite RFI choke suppressors - going to put some on the cabling off the ballasts, and some on the back of the head unit, see if it knocks it out.
Strangely, this morning, the RFI almost completely disappeared for a minute or two, then sort of phased in and out. It's a bit odd. It also seems to be worse on the lower end of the FM radio band.
I also installed my Osram Nightbreakers for my main beams - they are a bit brighter than the old ones, and slightly less yellow, but they're still nothing like a colour match for the 6000k HIDS!