added new muffler need advice

[drewtori]

hello i put a dual 3inch in/out megnaflow muffler on my 6.0 gas engine with no tail pipes or turn downs. i had glasspacks and it poped preety bad so i got this new muffler. iam wondering if turndowns will help the vibration and just air sound i am getting from the megnaflow. the megnaflow muffler was for me to quiet the sound down which it did but know it sounds just like air no sound any help thanxs possibelitys 2 3/4/ inch turndowns for a little backpressure? thanxs