In isolated instances, APC customers have observed a single beep being randomly emitted from their UPS products.
Back-UPS and Back-UPS PRO
In the majority of these cases, it was determined the UPS had transfered to the On Battery State (powering the load from internal batteries) momentarily and returned to the Online State (utility power) before the Onbattery notification (4 beeps every 30 seconds) could be completed.
The purpose of the Onbattery notification is to inform the customer when the UPS has sensed a power anomoly and has begun to power the connected equipment from it's internal batteries.
If a customer observes their UPS switching to the On Battery State frequently, an adjustment to the UPS thresholds for transfer may be required. Customers may reference the steps for adjustment of the UPS in their product's user manual.
Note: In one customer's case, we had observed the UPS emitting a single beep, once every 5 mins exactly. Upon removing the internal battery and reconnecting it, the beeping stopped. Upon testing, the issue was unable to be reproduced.