XDFilt is a Windows application program for filtering and removing noise
from audio signals. The audio source can be saved .wav files, external
live input as from a radio receiver, or external prerecorded material
as from audio tapes, phonograph records, etc.


XDFilt's features include:

- Adaptive removal of uncorrelated (random) noise.
- Adaptive removal of correlated (whistle/heterodyne) noise.
- "XD" adaptive removal of random noise.
- Point-and-click graphical user-defined filter.
- "Waterfall" spectrographic display.
- 'Live' input from radio receiver, cassette player, turntable, etc. to
standard PC sound interface.
- 'Canned' input from saved .wav files.
- 16 bit sampling. 8 k-sample/s sampling rate.
- Signal strength meter.


The distribution package includes examples of noisy signals in .wav
files.

And it's free.

http://www.saharlow.com/technology/xdfilt/index.htm