Ok guys and girls, I have a question. When I accelerate, my muffler vibrates very very bad. I know it is not the hangers so I have already ruled that out and it does it in every gear. I was told to check the donut baffle or also to check for a hole. When I first accelerate it vibrates badly but as I accelerate it goes away. I was also told it may be a compression issue. So I am at a loss as to where I need to start. Also would that cause me to have very poopty gas milleage? Oh another thing, when I start the car and let it idle, it sounds like it is putting. I know that sounds weird, but what I mean is that instead of a steady sound coming from the exhaust it is more of a putt-putt-putt sound. If I can record it and upload it I will do that instead of me trying to explain it.

"All men are created equal, only a select few become firefighters"

An exaust rattle is usually from your exaust hitting something under your car..... on 3rd gen J-bodies.... aftermarket exausts like to rattle againd you rear suspension on the drivers side if your mounts arn't adjusted just right.

Exaust leaks will give you that phoot phoot sound.

Going by your profile... it seems like you probably have a stock exaust....

My first guess would be that your downpipe is rusted or loose and leaking somewhere causing the exaust leak noise and rattle.... but I couldn't be sure without looking at it.

Also check the catalytic converter, it could have overheated and the contents could have blew on the inside.
This will cause @!#$ty gas mileage.