[Snake2998]

Thanks for the comments. I did note spdrakes comment - I am pretty sure it's not the bendix contact sticking as there aren't any problems with engagement or disengagement of the starter. The starter motor is not making a powered type noise, but just a winding down type noise. I have experienced the problem with a freewheeling motor when the solenoid failed leaving the motor permenantly powered (fortunately without engaging the bendix) - the only way to stop it from running was to turn off the battery isolator switch. This is nothing like that but definitely just an unpowered motor spinning down.

I will however take note of the comments and pay more attention to the symptoms.