Did you replace the oil filter? I would suspect a filter problem if you suddenly have low pressure, as there is an internal seal that will dump the pressure feed back into the pan through the bypass filter return if bad. No reason to expect that an occasional oil filter is defective, especially today. Get a Wix, Mann, or Knecht, avoid Bosch as they are now made in India with very erratic (if any) QC.

Your oil pump cannot be starved of oil unless there is none in the crankcase or the pickup tube is shot, it's not oiled by the pressure main.

Main bearings, on the other hand, can be oil starved and badly worn, causing low oil pressure. They will knock badly then, too, but you wont' mistake that for noisy lifters!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!