Okay, truck an 04, 1500 Z71 ext. cab and has 320k miles. Original front end. Today, almost all the way to work (20 miles) started to get a faint grinding from the front end. When I got to work, looked for obvious stuff stuck to the axle, but nothing. Going home, it was quiet at first, but after 20 miles, same noise. The noise is almost like that of the 4wd being engaged on dry pavement. When I turn to the left, it does get a little quieter. When I turn to the right, a little louder. It's not a clicking noise. So tonight, I changed the fluid (just in case) with Mobil 1 75w-90 synthetic. The front differential looked low, but no obvious leaks. the drain plug magnet has some metal filing on it. I washed the underside around the axles, wheels, etc, and checked my air pressure in the tires. Noise is still there. Noise doesn't change when I apply the brakes. Recently, on Friday I had to drive through some high water on roads (12" or so). No problems. Saturday, picked up a few yards of mulch that ended up sitting in the back until Sunday. Truck wasn't driven more then 2 miles with the mulch and haven't had problems in the past with the load (and not sure it's connected at all, but figured I'd include it). 4 weeks ago, I replaced the rotors, pads and calipers on the front end (along with rear rotors and pads). Noise doesn't really change if I'm in 4wd or 2WD. There is some play in the forward drive shaft that indicates the U-joint needs to be replaced, but that should even be moving in 2WD. so, I'm guessing it's a worn out wheel bearing from the driver side front or possibly the front differential. Any other tests I should try?