ooh had a bit of a brain wave... is it a kind of ventilator alarm?! or am i going bonkers?
That's what I thought too. I've heard it recently (when my brother was in ICU) and I've been trying to google ventilator alarms to check if I'm right, but haven't had any luck.
It sounds like an alarm I heard when my partner's grandfather was in hospital, regarding air in the IV tube. No idea if it's actually the same though, just similar.