intestinal rumbling caused by moving gas
"[The album] Earth 2 plunges you into the belly of a mastodon after a huge feast, and the sound is like the ensuing borborygmus." Dave Segal, The Stranger, May 30, 2012
About the Word:
Borborygmus is onomatopoeic, or imitative it sounds like the thing it describes. It's a New Latin word (Latin as used in scientific description and classification) that comes from the Greek borboryzein, "to rumble."