The burbling, rumbling, spluttering and other array of sounds that emanate from down below… what is going on to cause them?
I mean, if you extracted some stomach acid into a beaker and dropped food into it, would you still have those noises?
No you wouldn’t get the noises in a beaker… maybe a bit of fizzing if you put in some alkaline “food” as you get a neutralisation reaction.
The noises are the food being sloshed around, squeezed etc by your stomach muscles, and progressing along the digestive tract. There are some pretty strong muscles down there, which contract in waves to move everything along by a process called “peristalsis”. Air bubbles that you swallowed with the food will rise to the top, adding to the symphony, until you belch them out 
There’s not a lot of detail in it, but there is a Straight Dope Staff Report on the subject: Why does your stomach growl?
Damn Cecil, I was hoping I’d be the first to whip out borborygmus.
Ditto. It was the (very good) name of a mate’s (very bad) band at University (27 years ago). He was, not surprisingly, a medical student.