04 Mach 1 exhaust rattle
My 04 Mach without cats - exhaust rattles while at about 2800R's in second or third gear coasting (not giving any throttle) driving me nuts - any ideas. Mufflers are new - thought that was the original problem but it didn't change anything. 36,000 miles. New to me 1 year ago - sits in garage all winter.

I am not a late model Mach 1 owner so I have no personal experience on which to call.

Does the rattle sound like the exhaust is hitting up against something or does it sound more like a broken baffle in one of the parts?
The mufflers are new, so maybe not that. You removed the Cat's, so it cannot be that. By the way, aren't the O2 sensors going nuts without the catalytic convertors? Mainly the O2 sensors downstream of the Cat's? Was installing high flow cats as opposed to removing them not an option?

Anyway, what is left are heat shields. Climb under the car and start pounding/tapping on the exhaust from front to back and any shield you can find. Usually use your hand or a dead blow hammer. The dead blow hammer works good to pound on the exhaust. It is still possible something is loose inside one of your new mufflers.

With some issues, like this one, there is not much diagnosing and you have to jump in and look for something that is not correct.

Best Regards,
Thanks for the input - I took it to a muffler shop - they used the term "resonating" does that make sense to you?

The cats were removed by the previous owner - trips the 02 light often. I just turn it off when it bugs me.

Sorry, forgot to answer your ?s.

I sounds like a loose heat shield - but cant find anything loose.
Yeah, some mufflers resonate a lot and at some pitches sheetmetal items will vibrate and rattle. This is more common with chambered mufflers, like Flowmasters. Flowmaster has a "Delta Flow" style for most of their different series to reduce resonating and interior noise. THe small sized Flowmaster mufflers are worse. But unfortunately, the larger sizes won't fit. Straight through style mufflers, like Borla's, don't have that resonating issue much at all.

Large diameter exhaust tips also make the exhaust louder and with a deeper tone. That's has a big affect on why a late model car with a small V6 motor and an aftermarket Cat Back system is so loud. I don't like them, myself.

If it were mine, I would seriously consider installing some high flow Cat's or the originals. Reinstalling your Cat's, or high flow versions, will reduce the resonating tremendously and stop your check engine light from coming on.

My wife's 1996 Mustang GT, although older than yours, has Flowmaster 40 series with the Delta Flow technology and the original Cat's. Even though it has a deep tone at some RPM's there is no resonating.

Best Regards,
My 2008 V6 Mustang came from the factory with a y pipe into a single exhaust. I bought a complete set of GT duals that were complete, all they did was cut the V6 y pipe, slide the GT pipes onto the V6 y pipe, and weld it up. They did not replace the large weight/vibration dampener, to the Y pipe. My car was 6 months old when I installed this set of duals. The resonance at about 45 to 50mph was terrible, My wife told me to fix it or take them off. Since that wasn't going to happen, I cut the weight /dampener off my original V6 Y pipe and welded it onto the duals in approximately the original position. Problem solved and they're on the car to this day. This isn't the first car I've seen use a dampener on the exhaust, as some resonate worse then others. Hope it helps. Look under the passenger side of a V6 2005 up Mustang and you will see it in plain sight, right side about 6 inches before the y comes together. It should help. JTS 71 Mach1
Going to take off the chambered mufflers next week and put on the flow throughs. Have access to used ones to try - if it works - will put new ones on - gonna try that before going back to cats

thanks for the input
It should get better. If your lucky, it will stop all of it. Does the car at least have tail pipes? Or is your exhaust ending directly behind the muffler? If it doesn't have tail pipes, they would help. If it has tailpipes and large diameter exhaust tips, you might want to look into replacing the large diameter tips with something close that is close to the size of the tail pipe.

Why do you not want catalytic convertors on it? The high flow style wouldn't hurt the power.

In CA we're used to catalytic convertors on everything that originally had them. Actually, a vehicle cannot be registered unless all the emission controls are installed and operating correctly, all computer control systems must work correctly and tailpipe emissions while run on a dyno must be at or below the allowed maximum. These things are checked every two years and when a car transfers ownership.

Best Regards,
New mufflers on, annoying sound is gone, kind quiet now - unless I stomp on it. Can still hear the noise faintly - but now it doesn't sound like a rattle trap.

Thanks for the input!
Nice to hear new mufflers helped a lot! What kind of mufflers did you end up installing?

Best Regards,

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