About 3 months ago I did the timing chain and head gasket on my 1986 22re truck. Everything was fine untill recently it has been a little loud, i thought it might be the valves so yesterday i went to adjust them and they were ok. I happened to look down and noticed that the two bolts that hold the drivers side rail on were worn partialy. It only is loud after the vehicle warms up and when it is idling or there is no load on the motor. it goes away when there is a load on it. any ideas what may be causing this before i tear into it?

1986 xtra-cab 22re
stock everything
1991 bed