.. it is very much appreciated!
I changed the rotor and cap yesterday (it needed it badly) so I don't think that is the problem.
I did notice, however, that the protective cover just behind the bracket/rotor/cap was loose with the distributor cap off. I'm not sure if this protective cover is pressed back secure after locking down the cap or not -- I'm pretty sure it is. Besides, how would that type of noise suddenly disappear after reaching a certain temp?
I did tighten my poly V-belt and it almost sounds like the noise is coming from the air pump (one just above the alternator). Possible scenario is that the belt wasn't grabbing the pump quite all the way and not turning it as fast, but I'm sure I would've heard some slippage noises if that was the case.
I'll do some more investigation. Thank you too Yal for pointing me to that thread.