Random beeping noise

A small annoyance has cropped up with my 1.4 k11 and I was hoping someone may be able to shed some light on it.

When I insert the ignition key and turn it on, sometimes I get a quite loud number of 'bleeps' coming through the speakers, around 10 in total. Normally I wouldn't be too bothered and just live with it, however this is sometimes accompanied by a flashing airbag light. It doesn't happen all the time, and there seems to be no set pattern to when it does it, so it's a little perplexing.

I've checked all the airbag connections under the steering wheel (horn works ok so have dismissed the clock spring), seatbelt pre-tensioner connections, door switch, even the battery to ensure enough voltage by slaving in a brand new fully charged one of the correct rating. The 'key in ignition 3 times, 5 seconds on/off test' sometimes clears it, sometimes not. If it was a constant fault it would probably be easier to diagnose, there's just no set pattern to it.

I've sourced a replacement airbag control module from a donor car, hoping this may do the trick, though in the interim just wondered if anyone with more electrical knowledge may be able to steer me in the right direction. Many thanks.
My other Nissan from same era has a red light on the abs computer. It flashes error codes, I expect every abs computer has a flashing led if something is amiss.