the shop probably just uses the crappy spray to stop the rattling. what the spray does is dampen the sound just like dynomat. the only difference is that it's not a mat, and you don't have to lay it out and heat it on. You just spray and let it dry. The thing they don't tell you about that crap is that it can sometimes change the shape of the metal. In other words.. it'll deform the car. the only time i would use that is when u have dyno mat all laid out, and you still have some rattling.. then you use the spray on top of the dyno mat. and you make sure u don't damage the metal
