Magnaflow Rattle and Bumper Flaps

[Mack4]

I was showing my exhaust to some friends of mine today, and as I reved it up they told me they could hear a rattling noise, I got outta the truck and my buddy revs it and there it is. Sounds like something is inside of my pipe rattling around, like a penny. It happens at the tailend of the powerband, the exhaust peaks then, as it declines, I hear this rattling noise. I checked the Magnaflow clamps and they are torqued down really good, so it wasn't those, any suggestions?

Also, you know those little plastic guards that screw in under the bumper and onto the skidplate? What exactly are they for? Just to keep derbies off of my shocks? Would it be harmful to my brakes and suspension if I took them off?
-Mack

[HBjeff]

i had that exact thing happen on one of my trucks. cat was broken on the inside.

go underneath and smack your muffler and your cat real hard, i was able to hit the cat with my fist and hear the rattle

[Mack4]

I smacked my cat and muffler with a shoe, real hard, and I heard no rattle.
-Mack

[Mack4]

I solved it! Condensation in my exhaust was causing it to rattle. When I run the truck for short periods of time (school and back home) the condensation in the exhaust doesn't have time to vaporize. I took it out and ran my truck around town for about an hour and it burned off all the water- no rattle.
-Mack