Removed the underdash trim from under the passanger side air vent and with a little probing found the electric motor - remember we are RHD in Oz.

The motor lies on it's side in a frame but I was able to feel it revolve manually - I started the engine and the thing, as usual, screamed like a stuck pig but as soon as I flicked the rotor with my finger it started spinning without any noise.

I found a bit of the local insulation material had dropped and was lying over the fan rotor, very lightly, enough to stop rotation which produced the noise.

Hope this helps other long term sufferers.