Ron came into our room to give me the other baby (one was already in bed with me) and asked me what had made that sound he’d heard. Yeah, yeah, yeah… I often don’t know which is with me once I fall back to sleep.
So, anyway, I hadn’t heard anything, despite being awakened numerous times by the girls at that point (around 2:30am).
So, Ron checked on Joseph and Joseph was at his door (half awake) and told Ron that he’d fallen off the bed. So, the mystery of the sound was solved!
Why in the world Joseph fell off is another one altogether!