Ok, when I start up the car, it idles fine, when I give it gas, I hear a rattling sound when the engine is reving up or down. When I replace the clutch, I grab the heat sheild by the muffler and nothing was lose. What should I look for? I cant seem to find where its coming from.

 

put the car on ramps and get under it and have someone rev the engine to the point of noise. (safty first make sure the car is secure). It might be a rock in the heat shield. also look for contact points on the pipe.