I've got a 1998 4.6L. I'm reading the common P0401 code meaning insufficient exhaust recirculation. I bought the truck in March and since I've had it, it has always had this farting sound from the drivers side under the hood right after I shut off the engine. The sound last about 5 seconds. The code has just recently started popping up over the past few weeks. I've noticed rough idling, particularly in reverse, which is also new. From reading the internets, I'm pretty sure that some component of the EGR system is wigging out, but wanted to ask you guys if the farting sound is indicative of a specific component? Valve? Solenoid? Tube? Just clean the intake? Any help would be much appreciated.