Flex plate problems

I have fixed my son's s-10 4x4 6 times now and the same problem occures, The center hub of the flex plate breaks free from the rest of the plate after about 2 months of use. It starts out as a vibration that shacks the whole vehicle and eventialy breaks no bolts are found to be loose, the flex plates that I've put on are externally balanced and new. can anyone help, Thanks:banghead:

Does the starter make any abnormal noises when engaging or disengaging?

No the starter engages and works fine until the flex plate breaks.