Does the 02 envoy have a cabin filter

Yes it does. Behind the glove box. Here is a how~to video but you really don't need it, watch if you so desire but all you have to do is open glove box, (empty it out or everything will fall on floorboard). squeeze sides together until it drops all the way down and there is a black plastic box, pop the cover with a flat screwdriver and it's right there, will slide out and new one will slide right in. As for the musty smell. I have found that those Febreze clips that clip on to dash vents really do work.

www.youtube.com/watch?v=O54ZebfQixo .........forgot the video link