Im new on here. But I have had mustangs since i was able to drive... actually before i was able to drive. I currently have an 89 GT convertible and have just purchased a new 06 GT. I ordered the Axle back flowmaster exhaust and put it on, but there is this very annoying rattle right around 2k RPM's from the underneath, rear of the car. Has anyone else had this. I am gonna go investigating this weekend under the car but thought i would probe around here to see if anyone has had this annoying problem! Thanks! bret

 

We have the same problem on our 07 with JBA AB.

Have to take the whole car apart to find what is rattleing.............

 

Only vibration I have is change in my cup holder lol. Look under the mat in the trunk and see if any of the little replacement light bulbs has fallen down near the spare, that could be one source. That or the person who installed left the muffler a little loose and its vibrating itself.

 

I put flowies on before they had the kit, had a local muffler shop fix it up, and it rattled ALWAYS. Fixed the rattle by putting Borla's on. The rattle was at the top of the muffler, where it would hit the bottom of the gas tank. Not much clearance there, so the vibration would cause the rattle. The solution would have been to have someone fasion new, slightly longer hangers. I figured the new kits for the '05 would solve the problem, but apparently not. If you're in love with the flowies, find someone with a welder...

 

I noticed why mined didn't rattle. I have standard 40 series. The guy only used a hanger on the back of the muffler. He friggin permantly welded the front with a longer something, wasn't a hanger. Now I can't take the suckers off if I wanted to see what it sounded like with straights through cats. I"m thinking about taking it back to him and getting him to just put hangers on the fronts so I can take them on and off.

 

You won't find the source of the rattle by posting on a forum. The ONLY way to find it is to raise the car safely, get under and start shaking things until you find the rattle then figure out how to fix it. It will most likely involving loosening a few clamps so that you can reposition things slightly.

Good luck,

 

I remember seeing several earlier posts that described that some of the older Flowmasters for these cars had manufacturing defects and there were loose parts inside the muffler that rattled. Apparently flowmaster will replace them under warranty if that is the problem.

Another common problem is if the hanger rods on the mufflers are too close to the body of the car. When the exahust system expands due to heat and starts vibrating, the hanger rod can vibrate against the body of the car. You might check that too.

If it's not either of those two problems, then the other posters are right--start taking things apart and look for the rattle.

 

Well FACT is the Muffs are not the problem. Tons of clearance and I am not THAT stupid of a installer.

The Charcoal canister cover was rattling so I puts some Dynomat on it.
This is a noise cause by speakers and exhaust harmonics. Hoping maybe this was found/cured by a member.

We are taking the jack out wrapping that up, to take it out of the process.

 

hey thanks for all the fast and good info! Im hopeing this is what it is. It is directly above the muffler if not in it. Ill be getting on the task tonight or tomorrow night because when I hit around 2k RPM's it sounds like a rice burner with no mufflers. Maybe not as loud but still enough to erk me everytime i hear it!
Ill let everyone know what i figure out if anything!

 

Double check to make sure the mufflers are tight. After taking the car out and then restarting it a few days later I had a rattle and my passenger side muffler was loose. Flowmaster doesn't put a slit in their pipes so they are hard to compress around the mating pipe. I removed the muffler and slit it opposite of the line up slot. I reinstalled it and have had no problems since.