I had that problem when I replaced the stock muffler with a performance cat back system. I turned the MDS off on my truck with my SuperChips CORTEX Tuner. That was over two years ago. No more drone with all 8 cylinders running full time.
When I replace the stock camshaft and lifters, the mechanical/electrical parts of MDS will be gone too.
Not sure bought it after exhaust was put on guessing flowmasters most popular in my area usually cheapest but exits through the rear 45 degrees at corners of bumpers and big stainless slanted tips as again most common
05 1500 SLT Quad Black on Black | Pace Setter Long Tubes | Magna Flow Cat Back | Doug's Electric Cutout | Custom Ram Air Hood | Spyder LED Tails | Spec-D Black Projectors W/Halos | Jet 180 Stat | K&N CAI | 20 inch wheels | Comp 268 Cam W/6.1 push rods and springs | Diablo Trinity | Custom Tune by Charged392.
Welcome to HTC. I have a 2008 5.7 as well. I never noticed it but a buddy of mine was riding with me one day. We were coming back from Philly and were going across this steel bridge. We had the windows down and were driving next to the wall when out of no where he says, "wtf is wrong with your truck?" Come to find out it was the MDS. When I put my exhaust on it amplified it even more. Since then I have done a full delete of the MDS and that "underwater" sound has gone away. Most tuners these days allow you to turn it off.