Sorry, this rules out flexplate. May be gear or bearing damage in trans or transfer case. Remember, if noise is truck movement related, shift into (transfer case N-neutral) and give gas or see if knock goes away. Another test is to remove rear driveshaft and engage 4WD and drive around in front wheel drive. Caution, dont ROMP on it with just a front driveshaft, but see if noise is still present.
All else fails, turn up radio!!! Life is simple!!!
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