callahan

I had the same problem with my Borla mufflers. Nothing was touching causing the rattle. I tried all sorts of things. I believe that the rattle is caused by the frequency of the muffler's sound waves at certain rpms. I took a big old blanket and placed it under the carpet cover in the trunk. This has all but eliminated any rattle.

Rrruss

I had a rattle when accellerating after I first put mine on, I had to retighten the muffler clamp to fix it.

At first I thought the clamp didn't have enough thread on it to clamp tight, but backing it off and tightening it a few times got me and extra 1 to 1 1/2 turns and it has been good ever since.

jbt21479

I didnt have much time to mess with it tonight but did get under there and tighten the snot out of everything I could. Still have the rattle. But rest asured I will have this thing beat by the weekend (I hope!!) Just need to get the time to pull them back off and start the process of elimination! But this is exactly what i was hopeing for from everyone is all these suggestions so i have several options to try!! Here is a video of right after I installed them. You can hear it do it once for a split second when i rev it the second time flowmasters install

MBDiagMan

While you were tightening, did you shake everything to see if it was rattling against something?

rebelyell06

Yeah, when I was back at the place that put mine on earlier with a buddy, the guy mentioned something about the defects in the mufflers. My friend was having a 40 series put on and he noticed his 40 series was much, MUCH, bigger then my two(not put together). He had not cats and larger exaust tubing and my car was twice as loud as his. The guy who installed them was mad about it, but understood and told us why Flowmaster changed them, the defect deal.

05Retro

I heard the rattle in the video. Before you remove the mufflers get under the car and shake the pipe the muffler should move right along with the pipe at the connection as if they were solid any flex between the two and the muffler isn't tight enough. I had the rattle and someone else had the rattle also they were both the passenger side mufflers. Has stated in my previous post I removed the muffler put a slit in the pipe about an 1 1/4" deep across from the line up slot and remounted the muffler. No more rattle. The added slit lets the muffler pipe clamp down around the mating pipe. Make sure you use their clamps the stock ones won't clamp down enough. As for the defect I have not heard of anyone having the defect right out of the box the mufflers are new not bought second hand right. You can test for the defect by hitting the bottom of the back of the mufflers and see if you hear the rattle it should sound like it's internal. Let us know how you make out.