Yeah, the noise drives you nuts, doesnt it??
I found the problem to be a leaf stuck in the ventilation intake. Pressing the throttle would generate a slight 'nose up' angle on the car, caused the aerodynamics to go to pieces, and the leaf to whistle.
Lifting off the throttle, the nose dives, regains the proper airflow, and no whistle.
Could be your windscreen wiper (mine whistles under braking)
Hope this helps, as stupid as it may seem