2004 Dodge Durango Unusual noise (like a lawnmower) when en

No, the engine is not misfiring. I had it checked with an OBD2 scanner and ASE mechanic friend at the military base autohobby shop can't find anything wrong. The noise is only when engine is cold, after it warms up even at idle. Noise goes away.

I listened to it again yesterday and the noise is more pronounced at the lower section of the right side of the engine (as heard from the right wheel well).

The vehicle is not running differently. And the noise persist even more when driving as the engine is running at higher rpm. The noise however, goes away after a few miles of driving or when the engine gets to a higher temperature.

There was a check engine light but went away after I restarted the engine. The check engine light showed up over 3 mos back and never occured again.

Thank you for pointing me to the heat shield. I finally got the problem fixed. The noise was from a leaking exhaust manifold due to busted two aft mounting bolts. It was a quick fix ($46 for replacement bolts and gasket and 2 hours of my time.)