i had some grinding from my starter before it went out. it was the solenoid on mine that was the start of the problem. not to say that it is on your truck but if you need to replace that is kinda easy. only took and hour in the bank parking lot where is stoped working.
When your starter is working propely it shoots out a shaft with a gear at the end which is done by the use of a selenoid. the shaft could be binding up and not extending properly. Thus the gear is not fully engaging with the flywheel, causing the grinding noise
On an automatic transmission there is a flywheel right? And the starter on the automatic goes to the flywheel?
Just so I can organize my thoughts about how automatics work?
On an automatic, there is a FLEXPLATE. on the flexplate there are teeth. the starter, which bolts to your transmisson, has a gear that engages with the teeth on the flexplate. This is how the starter turns the motor over. If your starter is NOT engaging or meshing with the gears on the flexplate it may cause some type of noise which you are hearing.