Oil pressure drops as RPM's increase? Help?

I took my car to the dealership today. They hooked up an oil pressure gauge, and told me it was showing between 21 and 25 PSI at idle and then dropping to around 5 as RPM's went up.
Does anyone have an idea what would cause something like that? :banghead:

Sucking air from the pickup before the pump... maybe. Or if the filter is restricted. What is the rest of the story? Why are they checking oil pressure and what engine are you asking about? Are they using a mechanical gauge or a scanner?

They're checking oil pressure because my oil light keeps coming on. Using a mechanical gauge. There's also a loud sound coming from under the hood. Kind of like a whirring noise. It's a 2.0 liter engine. Thanks for helping.