Oil pressure comes up to 3 right after I start it.
However, once engine is at operating temperature (80C), oil pressure is down to "1" at idle. This is with 20/50 weight oil. Quickly goes back up when rpm is at 1200-1500 and above.
With thinner oil, oil pressure is a bit lower, maybe dropping to 2.5 or 2 when rpm at 2000 or lower.
Could the noise be hydraulic lifters that are stuck, maybe dirty? I have tuned my ear to the car over the years, and I swear I can hear the difference between 1 lifter (or valve?) and multiple lifters being stuck, and chattering. I can pick out multiple sources of the chatter, then the engine warms, the oil circulates, and the multiple sources of chatter drop off to one source, then that source finally stops.
It was a curious event that my mechanic put 20W-50 oil in it at the last oil change in mid-October. I thought he goofed, as I should be running winter oil now, 5W-30. Maybe he did it because he knows oil pressure in my car isn't great. I have been going to the same mechanic (family owned business) for the past 3.5 years. They only over-charge me a little and they don't make up extra work that needs to be done.