I've had the same noise for MANY miles. I thought it was the throw out bearing, nope. The I thought it could be the pilot bearing, nope. Short of tearing it down and completely breaking it, I live with it. The last time I had the tranny out (for the pilot and rear main), it sounded good for a few days with fresh oil in it, now it does it occassionly. Usually when cold and sometimes when turning left. Not usually when warmed up and going straight or right. Since I have another tranny I figured I'd wait for it to finally blow, but it has been a year or two, which means somewhere around 60,000 miles.
Both times I drained the tranny oil, there was no eveidence of color change or metal flakes that I could see.