There is an awful rattling noise that I hear thats coming from (roughly near) the rear left tire. It happens after I've been driving the car for about 30 minutes and when I idle. The car is an 91 EF STD hatch. any ideas? it has been lowered. im not sure what setup its sitting on though. I can get the specs if needed, I just would like to know what possibilites there are..

 

heat shield and/or cat?

 

My first thought on horrible rattling at certain RPM's. Check your exhaust header --> muffler

 

i found today that it was my muffler making the noise. i kept the car running and i went to my muffler and i held it up and the rattling noise stopped. im guessing something is loose?

 

well either the muffler is rubbing up against something, or if its a chambered muffler perhaps it is falling apart internally.