I have looked and looked again. How do you pop the top off. How much comes off the top and how. I see two places it might separate . about half way down looks like pull out tabs and then at the top ( with the air horn ) looks like screwdriver slots. How far in left field am I ??There is an auxiliary air pump that injects air into the exhaust headers when you start the engine from cold which has the effect of lowering the emissions until the cat gets upto temperature. The problem is that the bearings in this pump which is located just to the left front of the engine can get very noisy as they get older which can be very distracting. If you pop the top off the pump you can drop some light machine oil into the top bearing but is only a temporary measure. Some people disconnect the electrical connector to the pump to disable it which doesn't do any real harm as the pump was fitted to get around the ever stricter emission laws in various countries.
Hope that helps.