Flex plate crack

Hello. I'm an infrequent visitor here and so am not great at the forum search functions. I tried searching "flex plate" and "cracked flex plate", but got no returns. I have a 3rd Gen with a rattle that's been with me for a few months. It happens mostly after warm up and then at idle will be intermittent. I don't really hear it at above 30 mph. I was told it may be a cracked flex plate and that this was common in the 3rd Gen. I recently removed the inspection cover (that was a treat) and turned the engine over via the crack bolt. I saw what may be cracks, but very small. I couldn't get super close to it. My questions: what is a better way to search this? Are you familiar with this issue? I've heard there is a tool that uses powder and a magnet to find cracks, any idea what it is? Any other methods you're aware of? Thank you very much for your advice!

 

Yeah, this is a known issue in some cars.

Search string: "3rd gen 4runner cracked flexplate"

First Google Result:

 

Welcome from Wisconsin! I've heard of cracked flex plates before, not on the forum though, so I've never searched. The process you're talking about to find cracks is called magnafluxing, commonly used on engine blocks.. all kinds of metallic things, I'm not 100% sure, but you may need the part removed.