On the urging of a good friend of mine, against by initial better judgement, I acquired the the bike in a million pieces. The machine came home in a number of boxes and the box trailer of course. A giant 3d jigsaw puzzle, compounded by my ignorance. It has taken me about 3 weeks toying with it to get it started. 
My greatest problem was a frozen fuel pump initially, then a very dodgy main relay - which unfortunately only played up spasmodically.  Made a frightful mistake yesterday, did it while I had the multimeter in hand. Dreadful blunder.
I have played with Bosch motronic before, so I had a bit of a idea.... basic anyway - the movie is the thing going. The reason of my knowledge is in the back ground a 735i - I changed that from  motronic to Wolf3d and I am still none the wiser. So much for old age and wisdom  

If the bike is chucking out enough EMI to make that noise on the video, I'd be looking at changing the ignition leads.

You've got some high tension arcing and your camera sound system is picking up the RF. The motor seems to idle smooth enough therefore all plugs probably sparking so the arcing could be from a lead cap to the SP connection.

Faulty lead cap therefore lead not pushed on properly
Missing terminal nuts on the SPs. These don't come with NKG SPs but are required for standard K leads to make proper contact.

If a lead was earthing instead the SP would not be firing and the motor would have difficulty idling.
Just my 2cents worths

If its got the early coils they can do it too, known for it, sometimes it will still run smoothly. Coil cover off and running in dark may show it.

Also, if its an 8 valve engine it would should have resistor leads, possible they were changed out. But check the other items from Dai and KH first.

alby  had the same sort of noise  I think he changed coils .....his were '84 types that  broke down  internally and were jumping over to the engine just behind the coil packs