Right! It's part of the original production. It originated with Motown staffer Russ Terrana, who invented a sort of signal generator, similar to a Theramin. That's what Holland-Dozier-Holland used here - highly futuristic for its day, especially in the context of soul music.
A3 I heard this years ago and I think it was on the tour of duty soundtrack the electronic effects I thought it was a remix but now I know it's part of the song itself
I remember seeing one of these volumes carrying "St.Louis" by The Easybeats(licenced from the Australian arm of Polydor) issued as a single on Rare Earth as R-5009 in 1969. Music publishing handled by Robbins Music. There was no reference to ASCAP or BMI on the label of the single, but the track was included in one of these volumes.