Help with fixing problem with dc2

[mrjdm2u]

i have a 95 dc2 ls automatic and it started to overheat on me so i pulled over and let the car cool off and check the fluids in the radiator and added some coolant the temp gauge was fine as im driving it home now it starts to make a muffling noise when i press on the gas pedal and when its just ideling i can hear a rattling noise sounding like its coming from the exhaust piping that connects to the headers,help or any suggestion on what it can be