Just started the clackity-clack noise when cold then quiets to its normal diesel sound. What are possible causes? Also can't get the cross-over pipe off that runs from the air filter to the intake. I have removed the hex bolts on passenger side and the allen head bolt at the drivers side,but it won't budge. Am I missng something or do I just need to a longer pry bar? Thanks for your help.....

Larry..