2008 Expedition XLT clunking when accelerating and slowing down.

[ExpyOnly]

I have the same thing on my 2010 Expedition, usually at slow speeds I can hear a clunk, or accelerating lightly. Mine sounds like its coming from inside the transmission.
How many miles on your Expedition? If high mileage and still original trans/rear-end, my guess is that it is just wear on the drive-train, enough wear to cause a "clunk"

Merry Christmas,
- Joseph

I have 286,384 miles. Only drivetrain work done: I replaced the U-joints a few months ago. The clunking seemed to stop for one week and then return.