I added headers and 2.5" duals turned out in front of the rear wheels with super turbo mufflers. Not too loud. Not too quiet. All seems fine except when I get up to higher RPM's. I have no tach so I'm guessing pushing 4000 RPM when I get this bad popping sound like a rattling (bad) in the exhaust. Is this a classic case of needing a cross over pipe or H pipe? Ideas? Suggestions? Thanks.