In the G1 cartoon, soundwave was shown as a.... Streetlight.... in the first episode. He was also shown to dispatch Laserbeak shortly after so I guess in the toon at least they didn't need to be Cassette players. Don't know if it occurs in any of the other fictions tho.
but if you remember correctly, soundwave is the "streetlight" on cybertron BEFORE the left cybertron and crashed on earth.
after the crash on earth all you see soundwave transform into is a cassette player.....
just throwing that out there.