I have a 1997 GMC Sierra truck, It pops/clunks whenever i accelerate, and deaccelerate, it also pops sometimes when it shifts gears, but not always. It drives fine at normal speeds no problem, but when I get on the freeway and accelerate, it feels like something is slightly tugging back at the truck. It also pops when shifting at a standstill sometimes with the lever, its like an elbow pop, but for the truck, whats wrong? u Joints?