I havent yet, but intend too dynamat some of the trunk.
The plastic housing over the trunk latch with any subwoofer buzzs like a swarm of bees.

 

I'm not sure i get it... I can see trying to lower the noise from all the stupid rattles you might have. But to lower the noise from the exhaust? Why? Sometimes I just turn off the stereo and just listen to the motor and its wonderful growls!

 

Dynamat is not particularly effective at quieting down the exhaust, though it does diminish some of the constant buzz and hum. After I did my car, it was quieter at idle, but the sound when I really open her up sounds stronger. Of course, it's not acutally any louder, but when the noise floor is lowered, the sound of the pipes becomes more apparent.

It does a fantastic job quieting down rattles and also road noise. Road noise is the big factor for me. Reducing it allows the sounds you WANT to hear, like the stereo or the roar of your pipes when you nail the pedal, to be heard more clearly.

This is the #1 mod you will find with all serious car audio competitors, and for good reason.

 

CrazyAl you are exactly right. I am not an audio competetior yet, but my old car had a bunch a sound deading in it. Just check out my pics of my old stereo in my photobucket. That system in that car is slowly making its way into the mustang just have start sound deading again first.

 

I dynamatted the plastic housing on the latch in my trunk, that eliminated 90% of my rattle noise.
I need to sniff out the rest of the rattles, I can occasionally hear 1 more coming from the rear of the car.
But over all I'm very impressed how quiet my car is, and to be honest with the stereo nothing rattles ever.