Sort of on-topic, but I've coined the phrase "pseudosounds" for areas of tracks that actually create sounds that weren't really intended to be heard in the way they are heard. Now I hunt for them all the time. For example, even in my own work that I have produced, I have generated a mix-down of a track that has a split second where you can hear a bell ringing as clear as day, but taking apart all of the stems gives you no such thing. It's the combination of specific sounds in the stems that generate this effect, although it is not intended. ;)
Two that come to mind that I always thought were other instruments:
1: At 2:09 in Bohemian Rhapsody just after Freddie sings "... shivers down my spine", I always thought that was a wind chime, but on the 24 track you can here it's clearly Brian May scraping his pick either behind the nut or bridge.
2: The Doobie Brothers "Listen To The Music" at 0:36 and continuing for the rest of the song, what I believed to be a banjo turns out to be pan steels drums!!!