It would most likely be the wear tabs on your brake pads.Replace your pads
that makes sense,then i thought,a leak in the vacuum booster-just in front of driver side -in engine compartment-a rod comes into the vehicle and connects to brake. these can make a sound of rushing air-maybe whistle..so,there is a 2nd possible.
vacuum leak
When the wheel and the tire rub together.
Plugged catalytic converter
Check the fan belt; it may need to be tightened.
I would think that you have a leak in your exhaust system.
Low coolant causing air bubbles in the heater core.....
"Whistling" sounds are generally vacuum leaks. Start around the EGR valve and/or air intake de-icing assembly.
A defective vacuum line can cause a whistling sound when the vehicle is accelerating. A loose belt can also create a high pitched whistle sound.
A whistling noise indicates a vacuum leak.
A high pitched squeaking or whistling sound in the front right of a 2003 Grand Cherokee Limited V8 while driving could be due to a worn-out serpentine belt, a faulty wheel bearing, or a brake issue such as worn brake pads or warped rotors. It is recommended to have the vehicle inspected by a mechanic to diagnose and address the specific cause of the noise.
The problem could stem from anything so you would be best served taking the car to a mechanic so that they can look at the vehicle.
I have a 2004 freestar that also makes a squealing or "whistling" as I call it. I've had the ford mechanics look at it and they said the brakes are fine. I think it has something to do with the alloy wheels. The whistling starts on our van after it goes above 35 mph. As far as I can tell it's not a major problem just an annoyance.