Rust spots or signs of lack of lube. When you do it post some pictures and I or someone that knows what they are looking at /or for can help.
Former Ford Senior master tech, gas and diesel.1992-2012
ASE Master Tech, L1 certified.
2006 f250 cc swb fx4 6.0
mods arp,egr delete, tuned, 91 gallon RDS fuel tank.