The starter gear is always engaged. It does not move back and forth like a regular automotive starter.
Where is the noise you hear coming from that sounds like the starter spinning? If it is coming from the starter itself, then it is probably spinning. Coming from the side cover, it is the solenoid.
If the starter is spinning freely, it usually isn't good. Could be the;
1. failed sprag clutch on the hub/gear assembly
2. broken housing for the starter idler gear
3. broken teeth on one of the gears.
Make sure your battery is good. Hook up a charger to it directly. If that doesn't work, you might have to pull the side cover off to check the starter drive mechanism. If you do pull the starter, engine oil will come out.
Good luck.
