I got a F150 with a 5.4L and when I'm cruising down the highway every is goin well until I start to pull a hill. A loud fast rattle starts coming from the engine compartment, it sounds like it is mainly coming from the drivers side. The noise is really evident just before the truck down shifts out of OD, then its not as noisy and goes away when the truck is at full speed and not pulling a hill. The truck has lots of power and there are no check engine or fault lights on at all. The truck never hesitates. Interesting note, it doesn't make the rattle when revving the truck up in neutral. I really have no idea on this one and it is really starting to annoy the heck out of me when driving. Any ideas would be helpful me dearly. Thanks guys!