I have recently encountered a lot of people asking me to check up on rattles they here in their exhaust.  And although to some of us this may seem fairly elementary, many people do not even want to bother searching for the problem.  So I figured I would post some common exhaust rattle problems,

1.) The most common problem that I see is broken or cracked heat shields.  Exhaust systems usually have a thin material (usually aluminum ) either wrapped around the catalytic converter or mounted on the underbelly of the car to help protect the car from heat let off by the exhaust systems.  These heat shields tend to crack, or if two pieces are bolted together, often times bolts will work themselves lose.  When these events occur, usually you will start hearing a rattle sound.

2.)Stretched exhaust hangers.  Exhaust hangers are made of rubber and essentially connect your exhaust to the body of the car.  Over time these hangers can stretch out and become less firm from the weight of the exhaust.  If your hangers become elongated and flimsy, they allow your exhaust to a greater span of movement causing it to bump into other pieces of your car or the body of the car itself.

Hope this helps.  

if you have a cheaper exhaust that isnt made of the best quality parts it can also rust on the inside and cause the inside if resonators and mufflers to break down and fall to the bottom and rattle and the remaining parts left hanging around also tend to rattle.. you get what you pay for  

thanx! now I know more O_o