New Mopar Mini Starter Grinding (Clicking)

I have a new Mopar Mini Starter on my Mopar 360ci/380hp crate. It's had about a 100 starts w/ no problems. Then yesterday after stopping for gas, it wouldn't start. It sounds like the starter isn't engaging. I haven't checked to see if any of the starter bolts are loose as my jack won't fit under my newly lowered car (need a low profile jack).

The odd thing, I hooked some jumper cables to the battery (trunk mounted) and the car cranked without hesitation.

What do you think the issue is? The starter or the charging system?

I could really use some help. Thanks!