Hey Folks...
I have a similar problem, it has driving me crazy and it has done that all winter.
The whining or whistling sound when I hit close to 2000 RPM and stops around 2500. Sometimes a bit higher, sometimes a bit lower..
I have checked all the Vacuum, the PCV valve.
What makes it hard to pinpoint is that it does that only when driving. If I rev it up in the driveway, I cannot get it to do it.
When driving on highway, it is almost constant as on overdrive.. it goes around 2200 RPM
My truck is a Ford Ranger 1997 with a 3.0L automatic...
For a while I thought it was a bad ground and was coming out of the speakers..but I removed the fuse of the radio so it is definitely not that.
This is driving me NUTS...
I have recorded it with my MP3 players...
Crank up the volume.. let me know if it is the same whining you get
http://rapidshare.com/files/94048940/V0003.WAV
Cheers
Paul