Ignore it untill it fails. (the old 92 wagons has made odd noises for 80K) The 104 engines also have a pretty strong oil pump whine cold as well. Either way, untill it quits I'd leave well enough alone. The only serviceable part on the air pump is the clutch and the idler bearing will fail, however, thats a hot noise, not a cold noise.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.