My 2006 Mustang Gt has a noise coming from the rear of the car and i cant determine what it is coming from. When i first start the car up it doesnt make the noise then after the car warms up and i am just costing along and i give it a little gas it starts. It kinda sounds like a rattling noise at time then other times it sounds like a grinding noise. Another concern is my car is a automatic and when i have it in drive and i am costing i can punch the pedal and it will rev up and not accelorate. kinda makes it dangerous going through heavy traffic. The only mods that are done to my car is i have a superchips programmer that i set up the revlimiter and shift points and took away the top speed shut off. It has a Shaker hood scope and thats it. i would like to max out my cars horsepower in the cheapest way possable minus the supercharger, that will have to come later. Any advice would be much appreciated thank you.