This is driving me crazy!
 

I posted a thread a few days ago about a high pitch whistling sound... and here's some more info...

Another thing I noticed was when starting cold, I heard some cyclic squealing from around the belt accesories. The truck is still under the 3 month 3 thousand mile warranty I got when I bought it used from a Ford dealer so I took it in. The mechanic heard all the noises I complained about and identified the squealing as the idler pulley and belt tensioner. The parts had to be ordered and will be installed Tuesday. However, the mechanic could not idenfity the high pitch whistle. He is hoping that when he replaces the idler and tensioner, that will take care of the high pitch squeal. The problem is, I'm not so sure this whistling is belt-related...

The noise is very faint but it's so high pitched and piercing that it drives me crazy. It doesn't sound metallic, rather like air whistling or even like a really high pitch electronic buzz (it's NOT the stereo system). I hear the noise only when I take my foot off the gas when the RPMs are between 1500 and 2500. As the tach begins to drop, I hear the noise. I do not hear it when accelerationg or when in nuetral. Only under load and only after I take my foot off the gas.
Because it's so high pitched, it's difficult to pin point it's direction, but my wife and I have pretty much narrowed it down to driver side and behind the intrument panel. Is there anything in the dash that could be causing this? Or on that side of the engine compartment? I thought maybe EGR ports might be clogged creating a whistle but becuse the EGR doesn't work until the coolant temp is 113, I ruled that out because I hear the noise regardless of engine temp. I have ruled out the PCV valve as well. And it doesn't seem to be a vacuum leak either (dealer mechanic was sure of that). Is there somethign I'm missing? Could this noise be some sort of electromagnetic interference I am hearing? Or is the mechanic right, could it be that a pulley would make such a high pitch whistle under the described circumstances? I know you might say I should just wait until Tuesday and see what happens but this is going to drive me nuts all weekend. I don't have much confidence that the dealership is going to invest much time or money into correcting this problem because it only does it under specific conditions and the average person who doesn't care or know better might not even notice the sound. But I just paid $15,000 for this truck and everything else is immaculate; I don't want any little noises no matter how tolerable the dealership might think it is. I'd rather just solve the problem myself and be done with it. Anyway, any help you guys can offer would be great.

One more thing, I cleaned the throttle body with spray cleaner and noticed there is a little hole in the middle of the butterlfy. I put a piece of tape over this hole to see of that was the cause and I still heard the noise, so I took the tape off. I also checked my air duct (stock) and everything else I could find for proper fit and leaks.

No help on this one?

That little hole in theTB plate is an air caliibration so don't block it or you will have idle problems. This hole helps set the IAC operating range and plate throttle stop min. opening point.
I would say that you need to invest in a stethocope with a removable probe and use the handle part to locate the sound area then look at the offending situation. I have one of these and does come in handy at times for locating all kinds of noises.
Some times a transmission can have this kind of noise from the fluid flow thru the valve body ports and other areas due to the pressures involved. Not normal but usually dosn't hurt anything.
Sounds like a hydraulic system on a dozer, backhoe and the like.
I have a shift kit and done other valve body mods to an AOD in my blown Lincoln Mark VII that at times will howl and sing a small amount but not long enough to be irritating because I know what it it.
Good luck with it.