"since there is no smell it's not like they can prove you farted."
Jen, that is too funny!
I do the same thing as you. If my stoma makes a noise and someone is within earshot, I'll put my hand on my stomach (over the stoma to muffle the sound) and say, "Oh my goodness, my stomach's grumbling!" They'll usually say something like, "Yeah, I know what you mean, I'm hungry, too."
It works every time!