Sounds to me like the small rectangular anti-rattle pads that mount on the inside of the window to keep it firm in the slot.
The door panels have to come off, but that should be a combo of screws at various places (I'm stalling as I can't remember them all) including behind the door handle inside. 3 up inside the arm rest, one at the small piece end and 2 under the main pad. One at the front of the door on top and possibly one at the bottom on the back.
There is some factory GM goo that holds the sound deadener/wind block paper or plastic to the door, but it will come off if you pull the bottom out and then lift up over the sill at the top. It will come easy, so if it is difficult, you have not pulled everything. If you have manual windows, there will be a clip behind the center part that must come off (DON'T LOSE THIS). You can get a puller at autozone in the help section, or any smallish hook tool you have will pull it off.
It is a keeper clip, open at one end, that recesses into the handle to grab a recess on the window roller head. Pull straight back to you once you find it. Medium pressure is all you should need.
Finally, with the panel off, you will find the anti-rattle pads (or not) at the sill, bolted in from the passenger side. I doubt you will get these from a local parts store, but you can find them at most Vette supply houses.
If you need more detail, I'll be happy to take some pix. If you have a shop manual, it shows them but you need to study it a bit to get the feel of where the go and how to adjust them for best fit.
I'll be out all day, but will check back to see tonight if you need anything more or you can PM me.
Good Luck!