I'm not sure but I think I've narrowed it down.....When I shut off the motor, I hear a rapping, sort of like a valve opening and closing pretty fast for a second after shut down. It seems to be coming from the pass. side on the top rear of the motor maybe the fuel rail? Has anyone else noticed this?

Ed

 

Just a thought since i am changing plugs right now...
Have u changed plugs recently? I had to disconnect my pass. side fuel rail to get to the back (#8?) coil/plug. Maybe you did same and in process allowed an air pocket to establish in the rail...?

 

I don't know, Maybe the injector opens and closes a few extra times after you shut the engine down????

 

Havn't changed plugs, not 12k on them or the truck yet. I'll investigate more and figure out just where its coming from, its only that it is very noticable that I asked if anyone else heard it.

Thanks and I'll take any more ideas

Ed

 

is your air conditioner on prior to shutting off the engine? The a/c system will make a slight hissing/rattle noise while bleeding down.

 

it might be the fuel pressure regulater, do you know your fuel pressure?

 

I finally got a few minutes to check this out...it is the PCV Valve, when the motor is shut down the valve actuates very fast for a split second. I also heard the same thing on a 2000 f150....talked to a mechanic and he said its not uncommon...i guess i'll just keep listening to it.