Defeintly sounds stock to me. If it is the stock knob, yes, you take it off by twisting it. It can be vert tigh sometimes, but you have to twist it counter-clockwise about a 1/2 million times. Simply put, it is threaded pretty small, so you will have to twist it for awhile. It will come off though if it is stock.
There is one extreme though, it might be stripped. If that is the case, you're gonna have to prbably just pull it off. I doubt that is the case though myself.
On a minor note, congratulations on picking a Probe! Great car, and welcome!
If you think this is something, go to www.probetalk.com
It is NOTHING but Probes.