OK, here's a fun intermittent. The sound is what I would describe as a rotational grinding sound (gee, a chisel on your shop's grinding wheel might be a good analogy). Starts at 60-70mph, but it takes anywhere from 30 - 50 miles of driving before it starts. It will quiet down as I get under 40mph, does not come back if I try to run high rpms at slower speeds. Thought of a wheel bearing as the right front had a small dent in it, race was fine. replaced the bearing and still hear it. 4Crwaler isn't sure either, we've bantered about a couple of ideas. It seems like it comes from the front, but sometimes I can't be sure, maybe even rearward. Some upcoming work is to include a water pump (it's definitely starting to screech at first startup, I've seen some coolant at the weep hole on occasion), but with 170K on the clock it makes sense to go for the timing chain as well. There's also some u-joint issues where the rear one won't take grease, and the fitting won't come off, so likely some new u-joints. So....any other thoughts on such a noise? It certainly seems more drive train related than just engine rotation, but damned if I have isolated it yet. One school of thought has been that if it's so intermittent things ain't falling apart yet, so just play wait and see....