Sound Deadening, Stopping Resonance

Hello :)
Sound system is fine, but my new exhaust is part of the issue.
There is a little too much resonence during certain ranges. Nothing bad, but bothering me.

Its in an 05 mustang. The trunk design in relation to the mufller is causing the probem according to a lot of people.
Now here is my question. I have the trunk already covered with a layer of dynamat, but still pick up a lot of road noise and the exhaust. No rattles from the sub though :)

Would any kind of foam product absorb enough sound to help you think? Main question is that will any sound absorbing material affect the sub's sound in a negative way?

Looking at the stuff you use for studios / homes. It is a 2lb per square foot viynl mat. Also seen some foam products.

Figured I would ask the experts about sound a sound question. Hope you dont mind ;)
Thanks!!!
Steven

When I think of something resonating, I imagine it vibrating. So foam wouldn't be my first thought, as it won't add mass to this reonating panel which would cut down on the vibrations. You have already added some mass, so add some more until you are satisfied.

Foam would help out with simple road noise, not vibrations.

I couldn't imagine adding more deadening having a negative effect on the sub's performance.

Fatmat has a foam / rubber product that looks pretty good :) I thnk I will try a layer of that and see what happens.
The road noise is driving me bonkers. Nothing is vibrating, but the exhaust and the road noise together is too much.

Trunk and rear wheel wells have about 1/8 - 1/4 in of 3m sound deadening spray (complete coverage) and a layer of brown bread's product over that. STILL too much coming from the road. Ford "accustically designed" the cars so you could hear the exhaust..........big pain in the a##@# trying to stop it. They big break through - in the trunk under a layer of very very thin carpet - the only thing between you and the outside world is a piece of very thin sheet metal.

Thanks guys!