
I had the door liners off the toyota to repair the door handle/lock mechanism and install a tinted window I scabbed off the parts truck I had for a time...

I wandered over to grab a couple scraps of what is called "Ice and Water Shield" to keep ice dams from leaking into the house. I cut a few rectangles, 8" X 30" and 8" X 8". (2 Each) Peeled off the film backing and snuck it through the spaces of the door liner. Put the longer piece across the bottom of the door and the smaller one up near the door handle. And...

Sound proofed!!!
It doesn't sound like a tin can when I shut the doors now!
The stuff costs about fifty dollars a roll (enough to do about 900 cars) and sticks to anything!