I've got a single Flowermaster 50 Series SI/DO dumped before the rear axle and heard something odd over the weekend.

I got up in my bed to grab something and, as I'm standing at the front of the bed, I can hear this kinda "popping" noise coming from what seems like my exhaust.

Actually, it's more of a rapid "tonk" noise, (sounds like tonk,ta, tonk, tonk....[rpms go down and nothing]....ta, tonk, tonk....ect), and it goes along with the idol as it goes up and down w/ my a/c on.

You can't hear it from the side of the bed or underneith, you have to actually be IN the bed and hear it from above the exhaust between the cab and the bed.

Any idea what this could be!?

Oh, and it only started happening since I put my CAI on and the exhaust note slightly changed...

Any help would be greatly appreciated!

I'm no expert by any means, but I would think it could be the walls of the muffler resonating or pulsing if it only does this at idle or low rpm's. Hopefully someone else can support or disprove me on this one.