Coil whine is often associated with extremely high frame rates, at least in my experience. Setting a fixed FPS output is often the better solution.
Tools like MSI Afterburner or EVGA Precision will let you change the frequency and power behavior to some extent. You would simply reduce voltage and frequency until the problem goes away. This will reduce the performance of the graphics card.
Typically the switching frequency of the power delivery is fixed, so all you are really doing is reducing the amount of power that is being delivered.