Strange, LOUD noise after engine is turned off

[burnin oil]

Probably the starter hung. Next time you start it drive a few hundred feet and touch the starter. If its really warm the starter is toast. They will screech sometimes since the bearing isn't designed for cruise RPM. A side possibility is a worn ignition switch powering it in both state and run positions.
A throw out bearing can make a loud screech but can normally be heard above the engine. I can hear mine over 2 chamber mufflers when its acting up.