Noise Reduce has been specially written for removing constant noise from an audio stream.

Some of the features currently supported by Noise Reduce include:

• Support for reading and writing audio data at practically unlimited sample rates (including sample rates greater than 192000kHz)
• Support for using FFT frame sizes of practically any length enabling incredibly precise reductions – if time distortion is not a large issue.
• A reasonably fast processing speed with the codebase being developed in C++

Noise Reduce can be downloaded here

A brief usage guide for Noise Reduce can be found here