My truck came with an S&B intake installed and a straight pipe. I threw a muffler on the straight pipe in a quest to make highway travel more civilized. Now I can hear the low drone of the intake. I don't mind it around town, but on highway trips it becomes noticeable. So the question is how much louder is the intake vs the stock air box? Would it be worth it to throw the stocker back on? Will it cost anything performance wise?

There really is nothing to be gained or lost in horsepower with an air intake. Biggest advantage of a larger filter is you will see egt drop a little quicker. Where is your intake pulling from? Engine bay or is it cold air intake? Is it a dry element or oiled?

Intake temperature has nothing to do with EGT's only the intercooler does. The turbo discharge temperature will always be about 300-400*F at full run so what ever cold air intake your turbo discharge will still be hot. Stock air box are know for leaking dust because the plastic of the box will distort in time and not clamp down properly sealing the panel filter. This why I switched to the BHAF. As for the noise I would consider putting the silencer ring back into the turbo it will quiet it back down to a mild roar. Mine is obnoxious without the silencer ring while towing my trailers.

I'm not sure the silencer ring has been removed as the turbo noise really isn't that bad. However, I think what I am hearing is the actual intake pulse. If you are right next to the air box there is a definite low frequency pulse. The intake is an oiled filter cold air intake with an airbox around it. I wonder if the box around the filter is actually amplifying the intake noise and with it being situated so close the firewall, permeated the cabin? I guess I'll have to experiment!