If you guys want to reduce th "drone" to your straight piped exhaust then I have a little trick I learned.

The drone is simply a harmonic vibration in the exhaust pipe like a guitar string on a guitar. The larger or longer the pipe then the higher or lower the vibrations pitch. The Cummins seems to produce a drone on a stock straight piped exhaust at about 2000-2200 RPM. A muffler or resonator simply changes or removes the pitch of that vibration. Straight pipe exhaust drones because its long and straight with no variations to reduce any vibrations. So.....for a cheap and easy test, go down to the hardware store and get yourself 3 or 4 large hose clamps that will easily fit over your exhaust pipe and leave a little room for some other piece of metal. Then if you have a fence T post then great but if not, go buy a 5 to 7 foot long T post and remove the spade at the bottom. Then mount the T post to the exhaust pipe about where the muffler/resonator should be with the 3 or 4 hose clamps. I mounted mine to the top so its not visible. Then give it drive and I bet the drone is seriously reduced. You can also add more metal to the exhaust or a different kind of metal to see if it further changes the drone. I just chose a T post simply because it was laying on the side of my barn already and I was merely performing a "test" to see if it even worked. I just haven't found the time or need to do something fancier. This whole thing I just mentioned should cost no more than about $5 to $10 at the most. It wont change the noise of the exhaust outside the cab either. Just the level of the drone.

 

Interesting little bit of information there.

 

the mbrp makes a huge difference in the cab and still sounds awesome on the outside