Hi guys, bad news I'm afraid.
Firstly, yesterday morning after the car had been parked all night (near a path, so movement detection would have fired a lot), I came out to the camera beeping.
I powered it down, waited for the 3 beeps, and powered up. Held the mic button in to format the card, and all was well.
I then had a bit of a road trip yesterday, doing around 400 miles and for quite a long time period. Unfortunely 3/4 of the way through the cam again started beeping. I did the same reset process (while driving... Hmm!) and again all was fine (apart from losing data before the reset obviously).
S in my view, its card-full related.
That said, I will be sticking with it for now, as the low bit rate really annoys me! The quality of all videos I've taken, day and night have been exceptionally good.
Happy to test in a live environment if you want to try a different rate, and will try and remember to upload some night footage later.