That video was taken without the drive belt on. The radiator fan is fine, in fact I don't think it even runs during warm up.
It sounds very much like something internal. Not much I can do about it. I could take it to a BMW specialist here in the UK, but they mostly only deal with diesels and have likely not often opened up the valve cover to take a look at the valve train in an N52.
I feel guilty now for just installing an M3 steering wheel. Cost me about $190. Neglecting a difficult to solve engine sound only heard when cold and focusing on getting a better feeling in my hands...
