I own a 2004 expedition with a 5.4 liter engine. A knock has recently started which seems to come from the engine. The knock does not occur at all at idle or during normal driving regardless of torque or acceleration. It only occurs after pulling a long hill after cresting the hill and going to coast and only lasts 30 seconds or so. It appears worse when descending a long grade with the overdrive off and will continue constantly until accelerating or pushing overdrive button on then goes away. Have already tried to diagnose with chassis ear and have narrowed to upper engine or timing chain area. knock is loud very similar to a rod bearing knock - heavy metallic. oil pressure stays within specs with manual guage connected. Has anyone had a similar problem with any suggestions before I tear down to check cam phaser and timing components. Thanks for the input.