In this free tutorial video, Marcus Huyskens demonstrates how to use the Spectral Repair Module within iZotope RX, to quickly & transparently remove harsh "whistling" artifacts from speech without resorting to EQ, or a De-esser.
Want to know more about iZotope RX?
Mike Thornton has produced an extensive tutorial series on RX4 and RX4 Advanced that you can find on Groove 3
iZotope have also announced RX5 and RX 5 Advanced as well the the RX Production Suite.