Continuous "Morse Code" (or Popcorn) Sound (no smoke)

[Anonymous user]

My single Backups RS800 (new battery 3/15) has begun to make random continuous Morse Code sounds. (To you post-WWII members, that sounds like popcorn softly popping).
There are no blinking lights on the unit. There is no smoke or apparently unusual heat.
Unplugging the various units plugged in to the ports behind do not interrupt the sound.
Occasionally, it just stops for hours at a time and then continues like a teeny-tiny woodpecker in the walls.
When the unit is turned off using the push-button on the face, it goes quiet.
Any ideas would be dearly appreciated.
Many thanks

--jp