I can hear one of the motors that move the heater flaps behind the dash whirring back and forth as though it doesn't know it has reached the end of its travel. It is just a quick on off whir, fraction of a second only, always two of them-on/off--on/off etc. I have tried to identify which heater switch is causing and know it is not the windscreen air vent but having the other 2 switches either on or off makes no difference, but turning the fan to fully off stops it as I assume that switches off the heater completely.
It's one of those annoying noises that is not very loud but you know it's there, and presumably it will not get any better and will probably get worse until something fails.
Any ideas? I am thinking the dash needs to come out!!!! Or is there any easier way to get to this thing to see what is happening and what needs replacing?

Well, that brought a lot of response. Perhaps if I described the noise as a very faint dog barking ---woof woof---woof woof---etc
it might help

Hmmmm could it be a very small dog trapped behind there ? Try making noises like a postman through the vents and see if there is any reaction

I had to change my stepper motor.. Had the same problem.
There is a thread about it...