loud rumbles..IPS?

This is pretty common. I'm not sure it has a particular name, but if you're feeling fine I *wouldn't* call it IPS. As you have observed, it seems to have little to do with your pouch. Our small intestine gets rearranged to end at our pouch instead of ending in the right lower corner of of our abdomen, so perhaps that rearrangement makes for some unexpected twists and turns, and some noisy movement of intestinal contents.

It's called (gastro) colic reflex.  Basically 15 mins after eating your digestive tract starts contacting and stretching in order to move food through the gut (and eventually out).  The rumbling will be gas or liquid or both rattling through your non standard shaped bowels.  

Reducing gas forming foods and thickening your output would help, exercises to stretch and move the gas through the bowel will help as once expelled it will go quiet again, but that's something you need to do at home really.

Other than that afraid that's the way it is with a pouch, it might improve on time though

I definitely get this, and am used to laughing off the surprised looks from people nearby! I always assumed it was trapped wind (or wind moving through the small bowel, anyway), as it seems to co-incide with needing to empty the pouch within an hour or so.