Definately STOP
and rip it apart. I had the same sound the other day on the way home from wheelin and just thought is was somethign rattling. So there I am going 55 on the highway and my drivers side fron tire just locks up all of a sudden. Its a good thing there was no oncoming traffic. When I pulled it apart there was about 1/2 a quart of water in there and my bearing/race melted themselves to the hub assy and spindle. If there is excess play in the tire with the truck on jackstands you definately have a problem. And after you pull your bearings run them through the solvent tank and check for unusual wear. If there is replace as necessary.
