[audiomm]

I check the vane alignment first and make any adjustments (gently bending any offending vanes). The if the problem of noise persists, then I disconnect the wires to the tuning gangs and temporarily connect the HT in their place. A couple of rotations back & forth - accompanied by some fireworks/sparking - will clear any crud lodged between the vanes.
Job done and it works 100%. Don't forget to reinstate the wires and disconnect the HT :0