It could be cracks in the serpentine belt, they tend to make a lot of noise if it gets very bad. It can also be bad bearings on the idler pulley or one of the other pulleys or even the alternator or water pump or for that matter, anything else that's driven by the belt. Pull tension off the serpentine belt by backing off the tensioner. Manually turn each pulley by hand and try to find one that grinds or feels "rough" when you turn it. If you find one (or more) that doesn't turn smooth, replace it.
When you hit the bump, the mouse wakes up.
ball joints upper and lower control arm
Expedition Journal - 1999 Into the Blue was released on: USA: 1999
where is located ford expedition 1999 relays
5 per wheel on the 1999 Ford Expedition
Nine times out of ten it is a worn serpentine belt. Tensioners are also know to make a rattling noise congruently. Changing your belt and/or tensioner should solve your problem.
Expedition Journal - 1999 Map Maker was released on: USA: 1999
Expedition Journal - 1999 Wedded to the Wild was released on: USA: 1999
Expedition Journal - 1999 Kiss of the Spider was released on: USA: 1999
Expedition Journal - 1999 Above the Clouds was released on: USA: 1999
Expedition Journal - 1999 When the Earth Moves was released on: USA: 1999
Expedition Journal - 1999 Water Wars was released on: USA: 1999