I have similar issue on a milder side - mine does the rambling sound and it very seldom happen, no more than twice in short bursts for my short drive of 20 minutes to work. Sometimes, not at all, at least once most of the time. All hapenning at around 30-45 mph and as far as I know, never at highway speed.

From this board, it may be a torque converter shudder, and apparently, its pretty common for Ford vehicles, not only expedition. I bought anti-shudder transmission additive at Napa (the guy also told me that it is in fact pretty common for Ford trucks) and I will try to put it in as soon as a I figure out the easiest way to remove some fluid from my transmission. Its a bit overfilled as it is, and by adding almost a 3rd of a quart of the solution/additive I bought, It will be even worst (my transmission have been recently replaced and I hate it when the people who make a living doing this kind of thing do not do it right).

Anyway, I will not endorse any product, but I believe there are several products out there for the purpose - just make sure you get the right one. Just be sure to know what kind of ATF your vehicle require, don't just take the word of the guy behind the counter. I was initially given an additive that says for Mercon V, only to realize that mine only has Mercon. Some wise guys will tell you that that is an upgrade over Mercon, but manual says you don't mix them together. They could be right, but I will not take the chance. I ended up returning the MercV and getting the 'right' one for my transmission.

At less than $10, this is certainly worth a try (for me). Some good folks here did solve their issue with this. Other of course were not, and a host of other solutions were found, ranging from bad u-joint, bad LSD rear clutch, un-balanced or bent drive shaft, etc. I will start with this cheap one.

Good luck