HELP! CA18DET knocking?

The motor is making a clicking or knocking sound at about 3000 rpm only. It sounds fine at idle and I can't hear it at higher revs either. There is no loss of power.

I read somewhere of someone having the same problem with a CA, being a lack of oil to the head (bad oil pump). Someone else suggested rod knock. Any ideas?

could be a rod bearing, cuz i had a problem like that before on a old geo tracker.