I have an ABA VW gas inline motor in my 84 van,  turning a 5sp
tranny...with a diesel bellhousing and starter.   Been running this
motor and starter now for a few years as my daily driver, work van and
camper.   Every since I have owned it, when the engine catches and the
starter motor is cut off, there is about a half second of this strange
honking noise...I  don't really know the right way to describe it, but
it seems similar maybe to when you take a ping pong ball and squish it
down with the paddle onto the table...really kind of a brief
'squelching' noise, sort of.  Not loud, not alarming, just puzzling.
Anybody  want to try to guess what might be causing this sound?

   I figured, when I  first installed the motor and tranny and I heard
that noise, whatever was making the noise would soon cause me some
real problems, and then I could fix whatever it is....but it's now
coming on 3yrs of driving it like this, without even any indication
that anything is not right, other than that weird noise...The starter
works perfectly every time, but it makes that noise perhaps on 90% of
starts, always has...without any perceptible change in the sound or
the operation of the starter.   I have had the motor out and also the
tranny, to do a pilot bearing and a clutch... put it all back in and
there's that 'honk' again from the starter area.....

   Strange....
  Guesses? or better still, someone who actually might know what this is?