The Free On-line Dictionary of Computing (30 December 2018):

whalesong
moose call

   The peculiar clicking and whooshing sounds made by a PEP
   modem such as the Telebit Trailblazer as it tries to
   synchronise with another PEP modem for their special
   high-speed mode.  This sound isn't anything like the normal
   two-tone handshake between conventional modems and is
   instantly recognizable to anyone who has heard it more than
   once.  It sounds, in fact, very much like whale songs.  This
   noise is also called "the moose call" or "moose tones".