I must have heard the Beatles doing "Paperback Writer" a million times (although, as it is a "Paul song," I'm not particularly interested in it) ... however, tonight I heard something new.
Of course, I'm too lazy to go find the CD and see if it is on there, or if this is just an artifact of the MP3 or something, but ...
About 57 seconds into the song, there is the sound of a woman, not exactly moaning, but taking a rather sharp breath.
You might mistake it for just one of the Beatles taking a breath for the next lyric, but then you hear it again at a minute and 46 seconds, and it is much more distinct.
And now that I listen more closely, you can hear it a bit at the very beginning of the song, too!
I couldn't find any references to this on a quick net search, but I didn't try too hard.
The version I'm listening to is from CD collection of Beatles singles, Past Masters, Vol. 2.