I have a 04 Civic EX with 99,000 miles. For the last 20,000 miles or so I have noticed a slightly muffled rattle coming from the engine bay area. This rattle occurs anywhere from 1900 to 2500 rpm, particularly when the engine is under load such as pulling out while setting on a slight incline. Additionally, having the car in park and revving the engine to these specified rpm's will also cause the rattle. The car has given me no engine problems associated with this rattle for the past two years, and I have always assumed either something was loose or that is was the natural harmonics of the engine or exhaust ay that certain rpm. Any ideas on what this could be, other posts from separate forums seem to all be leaning towards the notion that a heat shield, somewhere along the exhaust line, would be causing the rattle especially on the catalytic converter directly under the engine. Any help is greatly appreciated. Thanks.