Creak when reversing the fifth wheel

If you have greaseable wet bolts, then they should be accessible without pulling the wheels. Some builders put them on the inside, so you might not see them right off. While Red and Tacky is wonderful for the zerks, B&W does recommend lithium grease for the saddle mount, as Cummins recommended above.

Creaking while backing/turning isn't too concerning, it's the bang that I would try the hardest to locate.