2002 4runner noise when engine starts after sitting for a long time. stops after about 15minutes driving

loud screeching that stops after the vehicle warms up can be a loose belt that stops screeching after it gets warm

yep, usually it is the alternator belt that is loose if it happens at startup and then stops after a bit. This happens because the alternator is trying to charge the battery back up after starting the car, in that time the alternator is under a higher load and difficult to turn until the battery is all charged back up which is why it stops after a few minutes.