It can damage the pinion gear of the starter and also the teeth on the flex plate, so if that is the cause you want to fix it sooner rather than later IMHO.
The photo below shows the clutch assembly from inside the starter. The toothed gear on the right is the pinion gear that extends outward to engage the
teeth of the flex plate. If the pinion gear shaft (located in the center of the clutch assy) does not extend or retract properly the teeth (pinion gear and flex plate) can grind against each other causing damage to either or both, IME.
The next photo shows the clutch partially disassembled with pinion shaft pulled out to reveal the small bits.
Note the long return spring around the shaft and the shorter spring to the right that fits inside the pinion gear gear.
If either of those springs or any other component is broken, weak, damaged, or missing, then the pinion
shaft may not extend or retract properly:
Worse case scenario if you knock off a bunch of teeth on the flex plate you could then have dead spots ie: if the engine stopped where the missing teeth on the flex plate were lined up with the starter pinion gear, then the next time you went to start the engine the pinion gear might not have anything to grab a hold of. The result might be that the starter pinion gear (that should extend and retract out while it cranks the engine) would just spin/grind but the engine might not crank (start).
Here's a previous thread discussing a loud noise when cranking/starting the engine:
Any updates here? I am also having the most horrendous sound at cold start. Sounds like what @george_tlc is describing. Only while cranking, sometime it stops the truck from turning over and next key turn usually makes no noise and it starts up.
The sound is no joke though. I have an aftermarket(autozone) starter with swapped internals. Sounds like I need to take it to my starter guy and check out both my flywheel and the pinion gear for damage.
It happened first a couple months ago, and has become more and more common over time.
