The whistle is either heterodyne noise or your picking up sound from a microphone type source.
Do you have a microphone plugged in? If so try tapping on it and see if the tapping comes across the speakers.
Try taping the unit, do you hear the results through the speakers?
You may be picking up cross-talk through a poorly filtered circuit, this may be caused by poor circuit design.
Try going to your audio properties and adjusting the line-in volume to see if this noise changes in pitch.
Make sure you do not have any wires or devices close by that are connected to or in the direct location, that can be causing the white-noise issue.
Broadcast Radio stations or continuous carrier devices can cause this issue to happen, it is RF interference.
You could have the device near a televison or other device with is emitting RF interference.
Make sure the electrical wiring in the house is polorized and grounded properly.
Edited by MrBruce1959, 07 July 2010 - 02:27 PM.