When adding MLV(mass loaded vinyl) the idea is that you're adding physical mass to vibrating panels in order to change their characteristics. Adding this mass doesn't stop the vibration, it just changes the frequency it will vibrate.
It doesn't have to be as expensive as others presume because they use a COVER EVERYTHING MENTALITY!!! Which is ridiculous. Don't confuse dampening with absorption or the attempt to block sound waves.
Foam typically only dissipates sound above 8khz. Majority of the song information is between 100hz and 5000hz. Do you need the toher frequencies? OF COURSE!!, for roll off etc.
Anyways, to get rid of rattle only cover 25% of the problem area to kill 90% of the rattle at the associated frequency. If you're trying to sound DEADEN/block sound, then you need to overlap MLV panels by a quarter inch when applied and create a wall of it. Then you dampen the sound with very thick and heavy foam. I believe closed cell is better in this application vs. open cell. When dealing with reflections...you want open cell.
So there ya go...JUST COVER 25% of the problem area. You'll be good to go.
