If you have opposing sides of the car vibrating at different frequencies, you're creating different soundwaves constantly trying to overcome each other. The resulting sound waves left over are called residual sound and would most likely be lopsided which would probably result in a bad sounding system. Sometimes, the clash of fighting soundwaves creates the static sound most confuse for distortion.
I was kinda more thinking doing the dynamat in the trunk and something else (second skin maybe? ) for the rest of the car or visa versa,