... three minutes into the song when Mary Clayton sings "rape, murder" the loudest, and her voice almost cracks, and in the background you can just barely (but clearly) make out someone (Keith?) shouting "woo!"?
Yeah. Miscellaneous trivia from Wikipedia: Merry Clayton reportedly suffered a miscarriage after recording the song; the intensity of her performance is alleged to have caused it. At 3:04 into the song Clayton's voice cracks on the word "murder" from the strain of her powerful singing. A second afterward an unknown voice, most likely Jagger's, is faintly heard shouting "Woo!" in approval.
This thread made me go and listen to the song again. I had never noticed it before, but now I do. Great song, BTW.