Hi Rob,
I am a big S type fan, hope to get one in month or two.
I have read of a similar problem.
Intermittent problems with air bag lights appearing , 3 beeps, not the horn sounding, quieter beeps.
The problem in that case was the battery.
He only did short trips after a good long run it cured the problem in his case.
Do you just do short journeys? was the car standing for a long tome?
Could be just low battery or need anew one possibly.
Best Rgds,
Julie.