I drive a 1993 F-150 300-six. A couple of days ago, I noticed a horrible rattling sound. It only happens when I am in gear. I can rev it in park and there is no noise, except the smooth sound of a healthy engine running through gibson cat back duals. The rattling happens only in drive or reverse, at low R.P.M.s. Is the exhaust the problem? If the exhaust is the problem, then how come it only rattles when in gear?

 

Where is the noise ? general area . Best way to locate where and what the noise is , Have a helper run the truck in gear while you look for the noise .Any heat shields on the exhaust ? . Noise is caused by vibration and vibration is the greastest while in gear because the idle has dropped .
Paul