Thanks for the replies,
Originally after reading through the forums, I was also thinking wheel bearings, which is why I replaced the left front hub assy, since it sounded like its coming from that area. I've done the normal checks for wheel bearings ( play in the tires, hand spinning ) & they seem fine that way. The new one I put on is a Moog brand & from what I've read are supposed to be pretty reliable. Its always possible it still could be the right front one going out ( even though there is no play or sounds when checking by hand ) & its just transferring the noise to the differential making it sound like its coming from the left side.
Looked at the tie-rod ends this morning & they seem fairly solid. I'm thinking that if it were suspension type parts going out, that I should be seeing some other issues like out of alignment, pulling to one side, unusual wear on tires. The truck drives straight, doesn't pull or drift to either side & the tires are wearing pretty even. Tires are 2yr old cooper brand, rated for 65,000. 35,000 on them so far. I haven't ruled out tire noise completely, but I've rotated them with no change to the noise.
As far as noises, the growling / roaring noise is really the only things I can really hear. Don't hear any clicking, popping, clunking. It does sound like a bearingish type of noise & seems to be loudest / deepest from 15 - 45 mph. Accelerating / braking doesn't effect the noise but does effect the speed of the truck, which effects the tone of the noise. Higher speed = higher pitch.
When I got home yesterday ( 40 min drive 65-75 mph highway speeds ), I crawled under the truck & felt for heat spots. The bearing hubs weren't very warm, although the brake rotors are pretty good heat sinks. The center shafts of the cv axles were cool. The inner cv axle joint cup was warm but not so hot that I couldn't hold on to it. The differential housing was hot, too hot to keep your hand on it. checked the fluid & its full. The front drive shaft was hot, but it also has the exhaust right next to it & pushing / pulling on it didn't show any looseness.
I also turned the wheels full left & right to check to see if the inner cv axle joint cups would move more than when they are straight. They didn't, so I think they seated correctly.
So I guess as it stands, some of the options are:
1) right front wheel bearing hub assy, transferring noise to differential.
2) cv axle inner cup joints getting worn out, but not enough to cause a clunking noise or a felt vibration.
3) Differential bearings / gears going out.
4) ?
