I do have the sentinel light feature. And there is the headlight buzzer and the seatbelt buzzer, of which the latter has not worked for quite some time. With the headlights coming on? I wouldn’t be surprised if the sentinel feature came on as you said which made the buzzer for it half go on or something. It was similar to a buzz but more of a whir/grind sound.
I really don’t use the feature at all, it’s more of a nuisance as I have to intentionally turn my lights off early or else they’ll stay on for 30 seconds and blind a neighbor or shine into a store’s window. Might be worth it to disable it if I catch the sound again. I’m most worried about the lights being stuck on at night and draining the battery.