How To Cure a "Rappy" Exaust?

My pickup had that annoying rap to it too. 2-1/2 pipe turned out behind the rear wheels. Tried several different mufflers, glasspacks and several other things but only got the thing to sound decent when I installed a crossover pipe. I was reluctant for clearance issues too. You can fit one up nice and tight if you plan the routing. Mine ran exactly in front of the transfer case skid plate. Never scraped the crossover once through a lot of serious 4-wheelin' in the mountains. (which did require the Warn winch on several occasions) Sounded great with the crossover and magnaflows. Nice deep purr that turned to a deeper growl on acceleration...none of that overly rich Chebby rappin'........