Hello. 06 Taho 5.3 chirp noise from under hood. changed belts still there. read some info about a Bulletin #PlP4138K anyone know of this. some kinda cam issue. thanks in advance.

Remove the belts and if the noise is still there good possibility you have a chipped lifter roller. Best way to narrow it down is using a stethoscope. Remove the valve cover and with the engine running, put pressure on the rocker arm in question with a wooden handle hammer (usually no.2 or 7 cylinders). If noise changes, its a very good possibility you have a cam and lifter failure. What happens is the camshaft is too hard , causing it to eat away at the soft lifter roller. The camshaft and all the lifters will need replaced and the engine oil changed.