Figaro marks the first time in a year I will not be running supertext for one of our shows. I'm actually only the backup supertext operator; our principal accompanist, Tom Webb, is the primary operator. So, unless he is playing in the pit for a show, he runs titles. By some funny circumstance, in the past few years we've had keyboard on almost every show. So Hansel & Gretel was the only show I saw from the house last year; before that, it was 2009's La Boheme. Gone are the days when I used to be able to sit in the house like a regular opera fan!
Anyway, despite being released from title duty, I won't get to watch this one either. For Figaro I will be backstage making noises. On purpose.
Offstage noises -- knocks, crashes, chimes, dings, whistles, wind, etc -- are sometimes made by stage management, sometimes by stagehands, sometimes by orchestra musicians, and sometimes by the singers themselves.
Singers will knock on doors. Percussionists have been known to play wind machines backstage (most recently, in The Flying Dutchman). Stage managers or props crews drop crash boxes.
What's a crash box? A crash box is, well, a box, usually a large wooden or metal crate, that holds an assortment of items and is dropped from backstage to simulate, well, a crash. Typical things inside crash boxes include cutlery, glassware, china, and wooden blocks. This website has an absolutely terrific description of how to create a radio crash box (which is smaller than a theater crash box, since they don't need the sound to resonate over a large space). I love his crash box recipe: