I'm a big stereo guy and my 03 obviously rattled like crazy plus it had 80K when I bought it. I removed all of the door panels and the rear hatch panel and added hush mat to everything (its a knock off of dynamat at about 1/3 the cost, buy it from summit) if installed properly where any plastic rubs metal your noise will stop.
I just sold the 03 and bought an 08 and OMG what a difference from the factory. As soon as I get a system ready to install im going to cover everything in it to hopefully keep it quiet.

 

I've had my 2003 H2 with 150k miles for just about a month now, and the cracking, squeaking interior KILLED me. So I went to work on them. I took them all off and flipped them over on a table (one at a time). I bought a bunch of plastic epoxy and placed it around all the connection plastics that make up the interior door. Over time the seams pop on the plastic welds that the hummer doors have. So re-enforcing them help out alot. Almost no cracking noises at all (from the doors). No idea how long it will last but its working well right now.

I had an idea tho. If you removed all the panels then scuffed up the plastics you could probably lace the back of them with fiberglass to make them wicked strong. Just an idea

 

My 2008 is really quite. We laughed when we first bought ours, that is was as quite as a Cadillac.

 

Speedometer stop working what could b wrong it turned on the other day but its off now