An oil pump is a pretty easy fix. But as you will read, you cannot fix the problem but a new oil pump should buy you some time. That is of course if you have an affected engine, have your oil pressure tested.

 

Add one more potential culprit to your list. It could be a slipped cylinder liner. My '03 has a loud knock and it is NOT the oil pump. I've had several people suggest slipped liner and the knock is either the rod contacting the liner or the liner hitting the bottom of the head.