Rattle in front end on my 2003 Tahoe Z-71????????

In June 2003 I purchased my awesome new Tahoe Z-71. I love every inch of it. But after a few months it developed a strange knocking or popping in the front
end area????? I was told that this was from a defective intermediate steering shaft??? And there was a recall. So I had it fixed last week. Still I can hear it pop a little. It is very odd. Does not do it over harsh bumps...only light ripples or slow changes in grade like humps etc..or turning while on a hill. How can I see to it that this stops? I love my car. Feel free to email me with advice.
Also...I have started my Z-71 on several occasions to have the 4x4 in neautral for some odd reason? And even more rare to have the circuits run slow...as in the gas gauge taking forever to register how much fuel is in the car.
Finally on several cold starts in the morning...my motor thumps right when the ignition is turned and starts the engine. Does not do this when the car is warm.
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