Recently my 94 xj6 has been making a rattling noise which sounds like it is around the torque converter. I will only do it when cold, once it warms up it goes away. The transmission shifts perfect. It sounds like a loose bolt being tossed around.
Could be the starter motor pinion not retracting correctly, I had that and thought that it was a cracked flex plate, sourced a secondhand one and had a trans place R & R it, when they started the engine it was doing the same thing, luckily the car was on the hoist and they could see the pinion sparking on the ring gear.
Is that regular, reoccuring little knock on idle?