Auditory hallucination

Auditory hallucination or phone being weird.

The other night I popped my sleep music on, phone on charge, went bathroom then I could hear a beeping noise from hallway. I traced it to my bedroom, to corner of room phone was in then phone to ear and it was from my phone. I unlocked it to check and couldn't see anything. No notifications and no alarms. Wasn't a typical alarm or timer sound either. I remember moving from my room initially thinking it was sons watch in his room and didn't hear it there, definitely from my phone. Can't find anything online so of course worry I'm going insane.