2015 5.3 horrible exhaust sound

[87_Corolla]

So I ordered a Borla pro xs muffler for my 2015 silverado 5.3. I took it to my exhaust guy and he welded in my Borla and welded a piece of pipe in place of the resonator over the axle. Everything else is still stock including the valve after the muffler. Inside the truck it sounds great, until you roll the windows down! From outside the truck you can hear air "wooshing" over the sound of the exhaust. It sounds almost like a horrible exhaust leak. Does anyone know if this is something due to the mufflers straight through design, or what? What gmc sierra exhaust system you also recommened? I called borla and they said it's because of the AFM and I need to buy the cat back system. It does it all the time not just when in V4. Any info on how to get rid of this horrible sound is appreciated.

[jimmyray]

So I ordered a Borla pro xs muffler for my 2015 silverado 5.3. I took it to my exhaust guy and he welded in my Borla and welded a piece of pipe in place of the resonator over the axle. Everything else is still stock including the valve after the muffler. Inside the truck it sounds great, until you roll the windows down! From outside the truck you can hear air "wooshing" over the sound of the exhaust. It sounds almost like a horrible exhaust leak. Does anyone know if this is something due to the mufflers straight through design, or what? What gmc sierra exhaust system you also recommened? I called borla and they said it's because of the AFM and I need to buy the cat back system. It does it all the time not just when in V4. Any info on how to get rid of this horrible sound is appreciated.

sounds like an exhaust leak from under the vehicle somewhere. Check the welds