Caller: Unknown

This number would call me everyday, when I eventually picked up, it was silent, except for a single hollow thud sound, similar to a flip-phone closing or a cell phone being put in its dock, it then would hang up. When called back it immediately plays a message in a female American accent saying "There is nobody available to take your call at the moment, goodbye." Afterwards it hangs up. I suspect this is an automated call that will call random numbers to test which are active by who picks up or calls back.