rattle?!!!!?WTF

The rattle may be a cracked flex plate or may be a cracked neck on the converter that goes into the front pump. Those stripped torque converter threads were supposed to be repaired with helicoils. It never a good idea to drill the holes in the flex plate larger or use a flex plate with "egg shapped" worn holes.
One more point I should mention... IF you use a longer bolts there and the bolt end dimples the torque converter case (behind the nut blocks) the converter can be damaged internally.