I respectfully disagree w/ you Sir. Why would the turbos have anything to do with it @ 0-1 PSI. Just to check, I went out and wrapped some towels around the vents...and it was gone and sounded 100% better. So back to my ?, what are most people using for the 3.5" DPF back?
How much to do you know about the turbo's on these trucks? Did you know that the sequential setup consist of an atmospheric charger and a VGT (variable geometry turbo)? Have you ever heard of a VGT duty cycle? Did you know that even when the turbo's are not spooled, the VGT duty cycle is active?
So....back to your question. A more thorough answer to your question would have been that the tubo's are the reason for the hairdryer sound and you will never fully get rid of it.
Here are your options though....
1. 4" downpipe back exhaust. It will slightly deepen the tone of your hairdryer sounding exhaust.
2. 4" turbo back exhaust. Once again, it will slightly deepen the tone of your hairdryer sounding exhaust.
3. 4" downpipe in to a 5" downpipe back exhaust. It will REALLY deepen the tone of your hairdryer sounding exhaust....but I assure you it will not rid you of it. This is the setup I have currently.
4. 4" exhaust w/muffler. It will just about make your exhaust as quiet as stock....and get rid of a good bit of the hairdryer. If your up for super quiet, go for that route.
5. 5" exhaust w/muffler. Probably the best option for dampening the hairdryer sound. It will still be there, but not as pronounced as a straight exhaust. Doing 5" with a muffler will also still give you that throaty hard throttle sound.
6. Swap your turbo's out to either a compound setup without a VGT or a single non VGT.
Hopefully this helps you out....and prevents you from wrapping a towel around your exhaust tip again.