Here's the deal.
Got a noise that sounds like its the heat shield under the passenger side front seat of a 2001 Expedition.
But here's what I need your help with:

Description:
* externally loud vibration noise
* ONLY at idle
* ONLY when in gear with the brake applied
* wife says she can feel it under her floorboard

I crawled up under the truck (mind you it was still hot, so I didnt go poking around the hot exhaust system too much), but the noise sounds like its coming from closer towards the engine compartment.

Anyone run into this and have a clue?
I know I need to go digging in the daylight, but jsut thought I would ask.

Thanks in advance.
Greg

 

could be a heat shield on the catalytic converter. common problem

 

I agree. Same thing happened on my 92 F150. Exactly what you described. My fix: I wrapped steel wire around the entire heatshield and cat. It worked but I don't expect you to do the same on an Expo. My F150 was a POS and falling apart.

 

Mine did that and it turned out one of my pipes broke loose up under the cab.