Ford Ranger Exhaust Intermittent Roaring

My 2000 Ford Ranger has an exhaust problem. When I go over a speed
bump too fast or hit a pothole, the exhaust begins to roar. It is not
like a cutout (that is like rapid gunshots), just a loud dull roar. Then,
when I go over another bump, it goes back to normal. I have had the
exhaust system inspected, and there is apparently nothing loose that
can be seen from the outside. I am wondering if there is something
loose inside the muffler and/or catalytic converter. I would like to
get a feel for what the problem might be before I take to a shop.

Thanks!

Glenn (ggentry)