my '03 Lightning has developed a very high pitched whistle. It is loud enough that you can hear it over the radio, no matter how loud you turn it up. The whistle comes in at 51-53 mph, 1720-1740 RPM then goes out....and comes back between 60 and 62 mph at around 1900 RPM give or take. How do I know the exact RPM & mph? From the little odometer flip trick I guess you call it. Any suggestions on where to look?

The outside air temp was 16-18 degrees F. Wind was at my back, steadily, at about 15-25 mph, but once I got to where I was going, I turned around & headed back the opposite direction (wind in my face) and no change in the pitch or volume. I didn't get a chance to put it in neutral & see if it was still there while coasting, but I did take it out of OD and it didn't seem to change. Once the speed drops below 51, it fades away quickly, same for when the speed increases past 53. The sound doesn't turn off, it fades away very quickly...and I can't hear any change in the pitch.

I JUST noticed it last night coming home from a bachelor party. I had not heard it anytime before that. I don't beat on my truck, I just drive it like an old man (trying to squeeze every last MPG out of it). It has 45,000 miles on it with new GY tires up front and old ones on the back....but it doesn't seem to be tire related because the pitch does not change at all, whether it's 52 mph or 62.

Ideas? Doesn't seem to hurt anything, just VERY annoying. The ladies that were with me didn't like it too much. Yes, it's pretty loud.

 

I assume it's not a door or window seal since they are easy to detect. Therefore, it must be coming from the front interior (my assumption, yours to confirm). Have you lost power? SES light? any work done lately? If not I would check vacuum lines going to the blower. If they are good then I would run it up from idle, while parked, and see if it makes the noise.
Belt slip? Does it shreak?
Just some random thoughts on what I would check.

 

Did you have your windshield replaced lately if so is the seal leaking?

 

No, I can't tell that it's any sort of interior or exterior air leak. I also don't think it's a vacuum line anywhere; it's a little bit different sound than that plus the engine runs very smooth. I would think that a vacuum leak would cause a little bit of running problems. It's kind of like the sound of a turbocharger's intake (the turbine makes an entirely different noise) at the onset of boost, only it is steady.

I drove it a little while ago, similar conditions except the outside air temp is a little warmer (34 F) and the noise is not there.

I dunno. I guess I won't worry with it.

As a side note, I did change plugs a little bit ago. Truck has 45,000 on it with the original Motorcrafts. I put in the TR6's. Engine runs a whole lot smoother now, the very slight shake at idle is gone completely. The job was not hard at all, it looked intimidating at first, but once you start digging in, it ain't all that bad. Took me a little less than an hour, and I was in no hurry at all. I also replaced the air filter...old one was not clogged, but a little nasty and I already had one so I said what the heck.