I unscrewed the sheetmetal gas tank cover because it was rattleing . I thought I cured my problem. But now when Im slowing down or sometimes when the cars in park (and running)I can hear a rattle, When I took off the heatsheild I noticed there was another shield above the exhaust pipe going over the axle, My question is how does that one come off? and has anyone had this problem

 

Not sure about that one, but it should just be held on by some sheetmetal screws like the others. You can either take it off or try cramming some aluminum foil behind it.

 

Maybe they put heat shields between the exhaust and the body and gas tank for a reason...
You should be able to fix those rattles. You could try drilling a small hole in the heat shield and putting a spring in it and hooking it to the car, that might prevent a rattle.