Well you can take the air pump apart and regrease the bearing.

Take the air pump off the mounts and on the back are 4 or 5 - 13mm bolts.

Remove the bolts and carefully tap off the rear panel - note there is a small mounting shaft near one of the bolts - give it some lub and tap gently.

The back panel will come off and expose the shaft, bearings and innards. Regrease or addsome, clean it up, spray on some rust inhibtor, line up the shaft and replace.

All is now quiet!

J