Jack the truck up on one side. Have someone grab the tire at 12 and 6 and you get under the truck and look while they firmly shake it. Look for movement at the hubs or ball joints. I had a tapping at 30+mph on right hand turns and then a screetching sound a few weeks later from my wheel bearing going bad. Involved pulling the axle, which was not a big deal and is definately a DIY'er at home.