Differential, CV joint problem

Here's the problem-
when driving down the road i hear a sound similar to driving down the highway and hitting rumble strips....like "waa waa waaa", like theres something rubbing the tire on and off, and it increases with speed. I have determined from spinning each front wheel individually with the vehicle on jack stands that it is the front left. On closer inspection of the left CV shaft, it is free to move left, right, up and down. The one on the other side doesnt move at all. I don't know how the front drivetrain is put together very well, could it be a bearing in the differential supporting the shaft? Any tips or insight into how things come apart would be appreciated as well.
Thanks,
Jon

Mine does the same thing but i havent looked into it yet. also when i take it outta 4hi i feel a violent pop a mile down the road. now ive tried all the scenarios to disengage it like as im driving, or in park, or in neutral regaurdless what i do it still happens...

The seat that the side gear rides in was worn out, you could put your finger in the output shaft hole and wiggle the gear around.