If that is the case, bed liner will be a total waste of money.
Great for protection, but horrible for noise reduction.
For noise damping, go with a combination of a real vibration damper, and a noise barrier.
Polyurethane coatings are incapable of absorbing vibrations, so they don't kill structure borne noise. They are also not efficient at blocking ariborne sound.
Use the right product for the given application and you will get much better results.