My recently purchased '05 Freestyle SE has a high-pitched whistling sound at speeds above 30-40 mph. It is quite annoying and very noticeable, both inside and outside the vehicle. It only seems to occur when driving on straight road and stops when I turn left or right. It sounds much like wind whistling through a wind tunnel - the pitch doesn't change - it's just there and annoying. Can anyone help, please??

 

There's something I'm having trouble with and that is do you really make turns at 40 MPH ? You probably are going slower than 30-40 so how fast are you really moving when you turn and the whistle lessens /stops?
Do you feel anything unusual in the steering wheel ?

 

I've heard of this before, and it usually denotes a noisey/worn (probably) front hub (wheel) bearing. This is a common complaint on Freestyles, though it really does need to be put up in the air and driven (my old favorite, the 'stationary road test') with someone underneath with a stethescope to pinpoint the noise.
If it's all wheel drive, just about anything in the drivetrain could cause it, but the clue was that it changes in a turn. Usually (NOT ALWAYS!) it's the opposite side that your turning to that is the culprit. Since these use double roller bearing hubs, it needs a good diag.