Does RT-AC3200 ever beep?

Something in my network closet randomly emits a 1 second beep, including 4 times last night. A few times, the router also rebooted.

Does the ASUS RT-AC3200 have audible alarms?
The User Guide doesn't mention that.
[It's running Asuswrt-Merlin version 378.56_0.]

I had fingered the UPS but I can rule it out after moving the UPS out of the closet.