When my car is in reverse gear and the clutch is down theres a clicking noise which speeds up or slows down in relation to the speed of the wheels.

It only does it in gear and is only really noticeable with the clutch down. You can just hear it when being driven backwards but its alot quieter and sounds different more like a rubbing noise.

Its done it for at least as long as I've had the car so not too worried and after a recent gear oil change there was no metal flakes apart from the usual metallic paste on the magnet.

Any ideas? Subaru dealership said either a tooth missing of the reverse gear or off the little reverse idle gear in the bottom of the case.

Have to say it hates going into reverse. Have to either pump the pedal and it snicks in or select another gear and then reverse - its like the clutch isn't depressed.