I think you might be thinking of the Theremin, staple of many sci-fi flicks. (A related, but similar-sounding, device has a prominent place in the Beach Boys' "Good Vibrations.") Could be that, or maybe just a manipulated tape piece.

The Mellotron was sort of an early sampling device -- a keyboard in which the keys activated a tape loop containing a short prerecorded snippet of an orchestral instrument. Moody Blues used it a lot. 