94 Jetta- Ignition 'whines' when starting (warm)

First, What a great resource this is! Thanks to all!! Ok, my mother's A3 Jetta (with AT, & 2.0 litre, etc.) has recently not started up on the first twist of the key when the car is warmed up (as it does quite well when cold). If after the engine fails to start on the first try you need to key 'back' to try again- usually two or three times before -what seems like- the starter being finally activated throughout the 'key to start' process. When the starter doesn't participate on those failed attempts you hear a muted 'whirring' sound (like a starter gear jumping out and spinning with nothing to contact). I am thinking the ignition switch or the starter itself may be bad since it seems unlikely that the starter would only select those 'missing teeth' on the flywheel when warmed-up. Hope this makes some sense. Thanks to all! Chris R.