I have a 2002 alero and i have two twelves in it, but the truck has a ridiculous amount of vibrations that sometimes ruin the quality of the bass, and sounds terrible from the outside of the car. I am just wondering if anyone knows if household insulation could help reduce that problem

 

Usually this is caused by a loose license plate.
I don't know of a household insulation product, but try a hardware store, there has to be some kind of adhesive backed flexible insulation out there.

 

These cars as well as grand am's with subwoofers commonly have the vibration. I would recommend a dynamat (or similar) trunk kit. I had put this in my cavalier last year, which had 2 10" Kicker Subs. This car also had a bad trunk rattle and was easily fixed.