Squeaky starter motor

Had a squeaky starter motor on my F7R'd Valver but never got round to looking at it, removed it today and greased the slide but it's still squeaky - any ideas what else it could be?

Im not 100% that is it the starter motor but it only squeaks on start-up and when switching off briefly which led me to believe it is the starter motor.

Thanks

More likely a pulley or aux belt.

Even though it only happens on start-up (eg. before the engine fires)? Surely if it was a pulley it would be constant?

Not necessarily.