I have the 5" turbo back and it does have a little drone at rpms around 2100-2300. If your looking for the same sound as a 5.9 you will be disappointed. You get more of a hissing kind of like a small jet engine because of the variable geo turbo, and it has 2 pre injection events so it is really quiet.
BTW. if you just straight pipe it by removing the muffler you will notice no difference as the puny little muffler is a straight through anyway. The DPF and 2 cats is what makes them quiet from the factory.