Just looking at one when the engine isn't running (torquing), it's impossible to tell if the vulcanized biscuit has separated from the metal mount. It has to be running and revved up while observing the mounts. Like I said, not expensive or a big deal to replace, unlike the new GM steering boxes are (6 hours labor and 450 bucks a throw), if you can get one that is.
Never heard one 'thump'. Have heard cooling fans hit the radiator shroud before however.
Like I said, replacement is easy. Jack up the engine enough to remove the bolts and replace.