i had the same problem with a silverline 4", instead of buyin a new system i cut the pipe off just past the bend over the rear axle and it stopped the drone. The drone in some of these systems is caused by the length of pipe "tuning" the sound to the resonate frequency of the the truck and in turn blowing out our ear drums. Try it, you have nothing to lose except the drone!
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2007 Mega Cab 5.9 CTD, Workhorse intake, 4" 304 Stainless Silverline exhaust, Fab Fours Rear Bumper, Lorenz Bilstein System w/firestone ride rites, stock wheels powder coated 285/75/17 Toyo E Rated At's. More on the way!