How do you check crank end play while all together? The engine and trans has been fine for 7 years. I dont see witness marks anywhere

Ok looked up how to check for crank walk,I can do that easy. I hope it's not that as that would be devastating.
the rattle is only in park though.could it be the converter is lighter in park due to less fluid being pumped in park so easier for the crank to walk back and forth?