2002 Jeep Grand Cherokee 4.0L - flexplate cracked. I had it replaced with an aftermarket brand not mopar. Pioneer I believe from o'Reilly's. Now the car makes a hard start noise like a quick grind sorta but starts fine and runs great! The mechanic says it's because of aftermarket flexplate. Is it not matched up with starter teeth size or what else could it be? Driving me crazy. Thanks

 

IDK about jeeps starters, but GM used to have problems with gear noise which required shims on the starter mounting bolts. You'll have to do some research yourself.

 

If the ring gear on the replacement flex plate is the wrong pitch it won't last very long...

 

It might be a problem with starter pinion engagement depth. AGAIN, my experience is with GM, but the standard transmission and the automatic transmission use different starters because of this. It's possible your aftermarket plate was made to FLYWHEEL specs.