When I have numb areas on my body, if they're exerted (especially hands and feet) they will tingle and buzz for a while afterward.

My guess is that you do have some numb areas in your tract, and the exertion is causing you to buzz in that area.

I've been having muscle cramps of various sorts all up and down the digestive system - from colon to bladder. So it's quite possible to have MS symptoms internally.

As to whether it's a warning... well, warning of what? Just keep an eye on it (difficult, I know!) and be ready to rush to the room if you need to.