We have a 1/2 mile gravel road leading to our house, and we could really hear when the tires picked up gravel and threw it up against the wheel wells.
On the inside of the RAM Promaster van, we used one and a half layers of Kilmat — first we put a partial layer in between the ribs, then a complete layer over that and the ribs.
I had the wheels off to give access when working on the propane tank and I had some 3M undercoat on hand so we decided to mask up the wheel well and spray a couple of coats under there. There is already some factory undercoating, but we figured it would not hurt to have a few more layers of protection and quiet.
The first step was masking:
Next, I jammed my head under the van and shot the undercoating behind the wheel well rim spraying towards the outside of the car. This operation might be a bit messy:
Then simply spray a couple of coats under the wheel well: