Poor little Tink Tink..

Welp it happened to me as well now. I had not even had the truck a month and I experienced flex-plate failure.. Ugghhh. Atleast it wasn't my transmission like I had original thought.

 

Yup, that is one of the warnings in the Megathread:

• Strange rattle noises at back of engine, like marbles rolling around: Several people here and at other forums have found this issue where they describe the sound as loose marbles banging around. Then found their flex plate was cracked in multiple places. Ticking timebomb. Check it out.

Sorry it happened to you. Hopefully when it grenaded, it didn’t screw you too bad.

 

Any thoughts on how this happens? Were any bolts loose allowing deflection under the torque of the starter?

 

Based on the pics in the thread I linked above, it looks like material failure to me. Not dissimilar to the material failure that causes the 2WD trucks to crack their transmission crossmember. This is similar to what I saw in pics from the three people nice enough to post pics.

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Things that cause this:
1. Mismating trans bellhousing to engine
2. Crankshaft flange with excessive runout
3. Unbalanced flex plate or torque converter.
4. Loose torque converter bolts
5. Material defect in flex plate
6. Engine making excessive power for application - haha Tundra 4.7 yeah no!