They always will make some noise, usually like a vacuum cleaner for a couple minutes when cold, but eventually they go bad and either get very noisy before they die or just sieze causing "Mr check engine light" to come on.

If and when you replace the air pump, be sure to replace its check valve, above the exhaust manifold as well. The check valves eventually stay opened too long causing excessive condensation to collect inside the airpump where the water then has nowhere to go, not exactly a great design IMO.