I had this annoying problem that when I left the my 348 sit for any length of time and then start it, it would make this rattling broken bearing noise for less then a minute or so and then start going a way. It wouldn't happen if the car had been run and warm. the car had to be stone cold for it to make the noise. it came from the front of the engine, driver side. come to find out the alternator belt was the cause.... along with the idler pulley that tensions it. next time you happen to be under the car doing some work on it. See if the idler pulley for the alternator moves from side to side. See if the bearing is loose fit in the pulley itself.. anyway, new belts and a bearing, no more weird noises.
