My 2005 GMC Denali has a characteristic 'clunk' that is significant through the passenger compartment on startup. I've gotten used to it, but maybe shouldn't be?

I assume its from torque converter drain back - but maybe its a worn u-joint?

Truck has 140K miles and has the AWD system. What a fuel pig, the 6.0L gas is most efficient in converting gasoline to noise, not torque.