Saab Repair: Oil Pressure, oil pressure gauge, pressure relief valve

Question
QUESTION: After replacing the oil cooler on a 1994 900 SE Turbo, the engine sounds like a sewing machine for a few seconds when starting.
At night and low temperature, light tapping sounds as engine warms up. Day time, warmer temps and engine warms to normal,tapping sounds are much more pronounced...
In a nutshell, I have a heat related oil pressure problem?  
Could I have a blocked cooler or oil cooler thermostat (where is it) issue.
Thnx....

ANSWER: Blocked cooler-not likely. Why did it get replaced in the first place? There is a pressure relief valve in the oil pump, perhaps this is sticking, not allowing pressure to reach the entire engine?

---------- FOLLOW-UP ----------

QUESTION: Answer to
"Why did it get replaced in the first place?"
The cooler has a pin sized hole in the bottom of it and started smoking,(spewing oil all over lower engine.

The pressure relief valve in the oil pump. How do I get to test/repair this?

Thanks

Answer
Take the valve out of the pump and all you can really do is make sure it moves freely. If you have access to an oil pressure gauge you should check the actual pressure. The pick up screen in the oil pan going be plugged, not allowing enough oil to be sucked up.