I ran a search for this, but came up empty-handed. I've developed a pretty loud rattle that I've isolated to the right front fender. The rattle is tied to the vibrations of the engine and seems to be most prevalent under acceleration from a stop and deceleration back to a stop. It's definitely more severe when it's cold, making me thing that maybe it's something that warms up, expands and tightens up? I can sometimes make the sound when I hit the air filter box just right with my hand, I've also been able to recreate it by hitting the exhaust down pipe pretty hard with a rubber mallet. I had the car on a lift and everything obvious is tight. Does anyone know what is inside the fender that could causing this? It is definitely becoming more severe over time. It sounds kind of like someone lost a wrench in there and it's rattling like crazy! Any thoughts would be greatly appreciated. Thanks.