butt growl
When your intestines make a churning noise -- similar to your stomach growling -- but you feel it in your butt.
"Dude, did the phone in my back pocket just vibrate, or did my butt growl?"
Butt growl
A fart that you successfully keep from escaping but decides to let loose inside and resembles your stomach growling loudly but clearly is not coming from your stomach.
I held that fart in but everyone still heard my butt growl. I was so embarrassed when my butt growled in the middle of class.