CV joints do move when you turn, that's why there is a joint there otherwise the wheels couldn't turn. On a FWD car it sounds like popcorn when you make a turn. (Wait around in a Wal-Mart parking lot and you'll be sure to hear it on someones car.:laugh
The teeth on the joint are popping in and out of place. This being a truck that weighs more I would think the sound would be similar but deeper. Which is what this sounds like to me.
When the wheels are straight, the joint is straight and doesn't pop. It usually starts by only making noise when turning one direction and as it gets worse it will do it in both directions. As it continues to get worse, it starts to take less of a turn to make it pop.
I've changed a bunch of these on FWD cars, I've only recently been getting into 4x4 toys.
No offense taken, I defiantly think he should be checking it all out and not going strictly off advice from people off the internet.