I have raptor headers, high flow cats, and res. Down to single exit like yours. I had a high flow muffler. I liked the sound, not loud. But had a tinging at 3.5-4k(like honda farther cannon buzz) changed the muffler to a quieter one. Didn't fix that issue. And just havnt been back to the shop to change the muffler out, and figure out what is causing that noise.