Hi, I recently purchased a '98 Ram 1500 with a 5.9 magnum. It has the high pitched whistle from idle and up. It is more throttle dependant than speed related. I have replaced the PCV valve and run the engine w/o the belt. Sprayed carb and choke around the throttle body and intake gaskets and upper plenum gaskets. Doesn't seem to change the idle. Covering the throttle body doesn't change noise either. Pinching off the PCV line makes no difference, however, if I plug the fresh air side of the system, from valve cover to A/C'er the noise will gradually diminish and stop. The noise does linger a second or two after shutting off engine. There seems to be quite a bit of vacuum on that fresh air hose as well. I don't know if that is normal or not. I'd say almost as much as the PCV line.