I have had the same thing happen on my 2005 X5 4.4i. Odd thing was I took it to a friend's shop. His tech plugged in the diagnostic computer, found some old codes that my Peake didn't completely clear (none of the codes were related to the seatbelt latch). Upon clearing all the old codes and pending codes, my issue vanished.

I don't know why it work. I don't care why it worked. No more random chiming!

TerminatorX5 has great thoughts above, but if those fail, then try getting the codes read and cleared with a GT1 (or GT1 software on a laptop).

__________________
Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual