It's the 6 speed transmission. I've experienced this with every Ford vehicle I've driven that has a 6 speed transmission. I usually experience it when slowing down and accelerating again. Never a "clunk" but definitely a jerk. At least with the lesser speed transmissions you couldn't feel the transmission shifting.
Great advice, I agree. My Edge is paid for, but I actually plan to do the same in a couple years. Although with so many redesigns and new models I'm not completely sure I'll get another Edge. Will just have to see when the time comes.