I always enjoyed listening to various used reel-to-reel or cassette tapes I could pick up cheaply...just to see what the previous owners had thought was worth preserving (the same thing applies to old home recordings of the 78 era!). I think the oddest one was audibly a tape made while somebody had been...well..."being fruitful and multiplying!" Always wondered if the original owner(s) had taped themselves or whom...
Never found any old "airchecks," though...which was what I was hoping for...
Steven C. Barr