My 2001 XLT sup. cab. is finally fixed after two years. I took it to the dealer, they fiddled around with the AC but never fixed it. My local garage tried some other stuff that didn't touch it. This week they replaced the AC compressor, and and accumulator drier? (AC clutch problem)It fixed half the noise. A knock that occurred over 3500 RPMs. Sounded like a diesel knock! That cleared the way for another noise to become more pronounced. It was from the rear of the engine. Second noise was a screeching noise also over 3500 RPMs. Turned out to be a heater hose. It developed a restriction of some sort. Now all quiet, and engine sounds like new. Apparently the heater hose is a rare problem, but the AC clutch is more common. Has anyone else had these issues?

 

my motor is knocking also but it only is when the a/c comp. clicks on was urs dointhesame thing?

 

A/c compressor is common. Along with the retrictor in the heater hose corroding and then turning slightly then causing a bigger restriction. This the reason why Fords replacement hose use a plastic restrictor.