My 80 has brand new OEM shocks and front springs. The hangers for the exhaust have been checked and are fine. Yet, there is still a squeaking that comes from underneath that sounds like metal on metal - i can't tell which side it's on and I know it's an old truck and will never be quiet, but it would be nice to figure out what needs attention if it's not the suspension or exhaust, what is the next likely source? hard to diagnose because it only makes noise when driving...