I'm constantly amazed at the low quality of the stock materials used, even in relatively expensive vehicles. Some will have decent stuff on the center tunnel and then cheesey asphalt based coatings everywhere else. I've seen thick layers of plain asphalt, coated asphalt sheets that go through the paint bake (very common) and even asphalt impregnated cardboard that was falling off on the roof a Dodge pickup that was falling off after 6 months. Some of these things seem to have been designed to get you through the test drive. The asphalt on the floor of an Hummer H1 had turned into a stringy goo that I cleaned off with a plastic ices scraper. Except for the rock hard, backed on material that is meant to stiffen panels, I'd suggest removing whatever stock material you can. As ///M5 said, do not bother putting aftermarket damper on top of either stock damper or other layers of aftermarket product. It has to be in contact with the panel to work. Additionally layers are damping the layer underneath, more than the panel itself. I wish I'd know this when I started. My car was a test platform for a lot of materials. I followed forum "wisdom" at the time, applying layer after layer of various vibration dampers. Car was solid and all of those layers created a decent barrier but it was incredibly wasteful. Not to mention that the sheet metal is completely inaccessible so that even something as simple as PDR is impossible. Now that I've treated similar cars the proper way, I'm tearing out the old stuff to redo it. The proper amount of the right materials is easier, cleaner, less expensive and WORKS MUCH BETTER. Here's what I'm pulling out: That's right, 8 layers of mat followed by 2 layers of liquid. Terrible job.