Replaced the gasket around the oil pump, and the horrible clattering noise went away.
The oil pressure was GREAT until this morning. I removed the dipstick to check the level, the level was fine, but after replacing the dipstick the level on the guage dropped and got lower throughout the day...
Car's running great, except for that. Oh, it was about 10 degrees warmer today than it has been, ~64 F.