I'd pull the valve cover and check for oil flow to the rockers. If it is low or nonexistent then you know the gauge isn't lying.
Then pull the pan and check the screen/pickup tube,pressure tube, and pump in that order. If no problem is noted, pull the main caps down and check bearings.
If there is no noise it is not likely to be a rod, but mains can bleed off a lot of pressure before making audible noises.
