There is a spacer that is made of sheet metal between the motor and the gearbox. On some cars the opening for the starter is part of the spacer and it's all one part. On others it's in two parts, one big one for the motor/trans and a small oval spacer with a big opening for the starter and 3 smaller holes for the starter bolts. You might have the two piece one and the one that goes with the starter was left out. Since this started with the starter change your problem most likely is related to the repair. If you can get a good well lit view of the starter you should be able to see the spacer. It's thin about .045 inch thick. A mirror might help. That and what was mentioned with the shoulder bolt are the things that jump out for me. When I'm bolting up a starter I rotate the starter on that middle shoulder bolt and put it half way of the pivot distance. It's not much of a pivot but in the middle has always worked for me. Hope that helps.