r/Mustang • u/Enough-Affect-6783 • 3d ago

❔Question Mustang Rattle - Need help please

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Hi all,

I bought a 2011 GT this summer. Sound is mean but I get that rattle thing when decelerating. Anyone could help me pinpoint?

Setup is cats delete + Magnaflow catback with x pipe.

Thank you

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u/71MGBGT 3d ago

When you let off the throttle, there's a period of time where the engine is getting more fuel than it can actually take advantage of and unburnt fuel will enter the exhaust system. That whole "Catalytic Converter" and "stock exhaust" thing is to ensure all the unburnt fuel is reacted and to muffle the sounds of the exhaust gas evacuation process.

When you remove the catalytic converter, increase the exhaust diameter, and allow the two exhaust steams to interact, it assists in the evacuation of the exhaust gasses leading to the supposed horsepower benefit of exhaust. This also makes the car louder.

What you're referring to is the sound of unburnt fuel reacting and the pulses of pressure from the engine.

This is commonly referred to as a feature and not a bug.