I bought an '03 Convertible today. The shift knob is loose and rattles. I popped the pattern insert out of the top of the knob, but I still don't see how to tighten the knob. Any advice?

Try removing the T-pin and then rotating the knob clockwise one full turn. Reinstall the pin and you should be good to go. Instructions for removing the pin can be found here: http://www.conceptualpolymer.com/corvette_install.htm

Good luck.