While using some spray on rubberized undercoating on my truck it occured to me that this stuff added weight to any panel that it was applied to. Also the resonant freq. of the panel was changed. Having seen the little displays in audio shops for different mats and hearing the thud vs ping sound that one heard from tapping the little piece of metal I tapped on the panels where the coating was applied. Same dull thud sound as the display pieces. I know that this may not be as effective as several layers of the mats and such but couldn't it be used as a very low cost alternative. What are your thoughts?