So i have an automatic 2006 Mustang GT with a Roush M90 super charger and all of the upgrades that come with it, along with an aftermarket exhaust system from bbk and flowmaster. when I press or let off of the gas, there's a loud rattling noise coming from what sounds like the back of the car. it sounds kind of like a rock in a soda can, it only does it when i press or let off the gas pedal and you cant hear it when idle. does anyone know what it might be?

 

also, sometimes it wont do it at all and other times, not till you drive it for a bit.

 

I'm no mechanic but I would first look at any heat shield you may have. It could be lose. If that is not it maybe the resinator in the muffler is broken up? You should be able to hit your muffler and here it while the car is off.

Just a shot in the dark but worth a try before you send any money

 

I agree about checking the muffler. Got mine taken off last week on my 98 and it had a good bit of crap broken up in it.

 

thanks guys, I'll give those ideas a shot.