Hello, my name is ***** ***** I am going to assist you with this.
There is nothing in the rotor or stator that can knock, unless they are physically hitting each other.
The stator can not move at all, as it is bolted directly to the engine housing.
The rotor only has 2 places that it can move - the bearing end or the crank end.
If the bearing is good, and there is no looseness there, then you need to look at the crank end. You may well have a broken crankshaft, or a bad crank bearing.
Putting a load on the generator puts a load on the engine. If the crank is broke or a bearing as bad, it can easily create movement - and end up doing a lot more damage.
What you need to do is to remove the generator from the engine, and inspect everything carefully. If nothing is visible, try moving the crankshaft. There should not be any movement.