Exhaust rattle / resonance problem

[miata5620]

Ok I am posting this up so I can get some other opinions on what is going on with my car. My exhaust consist of stock manifold, FM catted mid pipe, and silverline cat back. Around a month ago my cars exhaust started to make a rattle/ metallic resonance sound coming from the cat back of the car. The sound almost seems like a sub woofer going off inside the muffler. I have figured out the sound comes and goes pretty much at the 1600-1700 rpm range and it will stop if I put my foot anywhere on the cat back. I have been under the car and inspected the exhaust and it is not touching the car anywhere and has plenty of room all around it and the rubber exhaust hangers look to be in good shape. At first I thought something inside the muffler had gotten loose/ a weld broke but then wouldn't it make the noise all the time instead of just at a certain rpm range. Anyone have any thoughts on what is going on here any help would be appreciated.

[FooSchnickens]

Try banging it with a mallet with the car turned off.

Also, how long have the aftermarket parts been on the car?

[miata5620]

The cat back has been on the car for about 3 yrs and maybe 15000 miles and the mid pipe has been on for 2 yrs 5000 miles. While it is my daily driver it really hasn't been driven a lot since I had my work truck at the house it really only gets driven on the weekends.

[jester911]

If it stops by touching it with your foot I would say the hanger towards the rear may be the cause.

[miata5620]

If it stops by touching it with your foot I would say the hanger towards the rear may be the cause.

Yeah I thought that too but after inspecting them both the metal hangers and the rubber pieces seem fine. The rubber seems good still not cracked or dry rotted. I might swing by mazmart next week and grab some new rubber pieces just to make sure its not them but I really doubt it is since they look to be good.

[jester911]

You need to isolate the rattle. Try disconnecting the hangers one at a time and checking it.

[— kung fu jesus —]

You might want to remove it and re-hang it. Inspect all the pieces, the gaskets, the connections and hardware. I've had a number of exhaust systems over the years, from cat-backs to customs. In my experience, the fewer connections, the better the fit (custom). The cat-back systems I've had that fit the best and had the fewest leaks were slip-fit (like the Borla). The ones with two-bolt flanges at the midpipe and rear section always gave me trouble at some point, like warping flanges, weak gaskets, build variances, etc.

It's also possible a piece of the cat broke off and is trapped in the midpipe.

[miata5620]

You might want to remove it and re-hang it. Inspect all the pieces, the gaskets, the connections and hardware. I've had a number of exhaust systems over the years, from cat-backs to customs. In my experience, the fewer connections, the better the fit (custom). The cat-back systems I've had that fit the best and had the fewest leaks were slip-fit (like the Borla). The ones with two-bolt flanges at the midpipe and rear section always gave me trouble at some point, like warping flanges, weak gaskets, build variances, etc.

It's also possible a piece of the cat broke off and is trapped in the midpipe.

If the weather is good I plan on removing it and checking everything out also want to make sure there is nothing inside it like part of the cat. I do agree with you that the slip-fit systems do fit much better, I had that on my mustang and it fit nicer and was more adjustable to clear everything under the car. If taking the exhaust off the car and checking it over and the exhaust hangers doesnt fix anything I might see if anyone local has a stock or aftermarket cat back that I can barrow to fit and see if the sound is there still. I have talked to the company I got the system from and he told me if it is something wrong with the muffler he will sell me a replacement one at a good discount but hopefully it doesn't come down to that.

[miata5620]

Well I uninstalled the system today and inspected everything and visually everything looked fine. Once I got the muffler off the car I took Foos' advise and hit it with a mallet ( gently) and as soon as I tapped one side of it I heard that same resonance that I was hearing with it on the car. I did shake the cat back around and nothing is moving around in there so at this point I am assuming part of the baffling or pipes inside the muffler itself has broken a weld and is loose enough to vibrate inside the muffler. I guess I will be buying a new cat back to replace this one even though it works fine that noise just gets on my nerve and I can't stand it.

[exdotcomer]

mine has that too- i think its the some shield above the cat

[miata5620]

mine has that too- i think its the some shield above the cat

I did check all the shielding on the car to make sure none of it was lose in my car I was thinking that it could have been the shield between the muffler and gas tank but after looking into it I quickly found out that wasnt the case.

[Soledad]

Mine also has the metallic rattle. It started doing it the very second I started the car after installing my Borla catback. I drove myself bat-crap crazy trying to isolate the source of the sound. It only does it at idle when it's cold, so I gave up trying to find it.

[— kung fu jesus —]

Retighten the clamps and bolts.

[Soledad]

Clamps and bolts are as tight they should be. My sound is coming from the muffler/tailpipe area. It sounds almost as if there is something inside the muffler shaking. Again, mine only does it when its cold.

[rattlecanmx5]

looking at the muffler tip there is a small metal corner that hides behind the bumper. Check and see if it is possibly tapping that. Mine did that untill I bent the hangars to make it sit closer to the passenger side.