I have a 1990 Jeep Cherokee with the 4.0L 6Cyl. Everytime after the engine warms up I get a high pitch whistling noise which sound like it is coming from one of the fuel injectors. I have used an auto stethoscope to check the bearings and that doesn't seem to be the issue. Usually if you turn the jeep of and let it sit for 5 minutes and then start it back up the whistle doesn't occur anymore. Also most fo the time when it does whistle, it also is idling higher than normal. Also anytime power is added, the noise goes away. If anyone has any info on this I would appreciate it.