1996 4.0 with 1800-2100 RPM Whistle?

[IlyushinYakovlev]

I have a 1996 Explorer with the 4.0L V6 and 214,000 miles on the odometer. (completely stock air intake, engine, and exhaust) I've had it since around 130,000 miles or so and since the day I purchased my Ex, its had this subtle but quite audible high pitched whistle that occurs without fail as the tachometer needle passes through the 1800-2100 RPM range in every gear including reverse. This noise occurs as I accelerate or slow down, and seems to have absolutely no relationship to external temperature or humidity levels. Though the whistle occurs only within a small RPM range, its tone increases/decreases slightly in direct relation with RPM readings within its specific audible zone. This whistle is simply annoying, and presents no real mechanical problem so far as I can tell. However, I'd like to correct it if possible. I've read a good deal about the "4.0 Moose Call" and a howling noise found in some explorers, but no description posted on this forum seems to match the noise that I'm experiencing. If anyone has any ideas, similar experiences, or suggestions for my annoying problem, It'd be great if you could share what you know. Thank you in advance!