Could be some worn teeth on the ring gear, or the starter drive might be too tight when engaged in the ring gear. Shims can be purchased from most auto parts stores.
If it has shims now and you buy an OEM replacement starter, then use the shims. If it does not have shims then you will not need them. Replace the starter with an exactly duplicate, installed exactly as the original. If in doubt measure the distance from the mounting plate face to the end of the drive gear shaft and make sure that distance in the same on the replacement starter.
The starter may require shims to correct that. The ring gear and or the flywheel may be damaged also.
Do not install the shims. Your starter should work fine.
One of the easiest starters ever... 1) Disconnect negative battery cable 2) Remove nut holding power wire to starter. 3)Remove smaller wire(s) to starter. Mark which goes where if several are present, and you don't think you'll remember how it goes. 4)Remove the starter bolts that are locatd directly under the starter. 5)Starter will come out of vehicle at this point. NOTE: Many Chevy's use shims to space the starter from the flywheel. If your vehicle uses them the new starter will likely come with shims. Use the same number of shims as was in the vehicle when you took it apart. If starter grinds when starting after starter replacement you may need to add additional shims.
between the starter and what it is bolted to
You should be able to buy starter shims at any auto parts outlet. If not their you could get them at the dealers parts department.
Check the backlash between the starter drive and the ring gear after installation. If it's too tight, use shims.
Disconnect battery. Then the electrical connection on the starter solenoid. Remove the starter bolts and the starter. Note the location of the spacer shims. Installation is the reverse. Don't forget the spacers shims or you will get noise when starting the vehicle.
There are several shims that could be used such as starter shims (for adjusting drive gear to ring gear), caster/camber shims (for front end alignment), body shims (for aligning body panels),
Shims bring the starter closer or further from the ring gear for proper alignment.
No, you should get new shims from wherever you got the new starter, but if not, make sure they go back into the same position they where. New shims, make sure they are the same thickness as the old ones.
The starter drive gear will be too close to the flywheel, causing a grinding noise when the starter is engaged.