Do you have the notch filter nyquist plug-in for Audacity?
You can find it here -----
http://audacity.sourceforge.net/nyquist/notch.zipHere's a wiki -----
http://wiki.audacityteam.org/index.php?title=Noise_RemovalHalfway down the page it deals with finding the offending frequency, and designing a notch filter. You can do what it recommends there (
the hard way).........you will have to enter values at the Nyquist prompt
----------------- OR---------------------------
(
the easy way) If you download and install the Nyquist Notch Filter tool, it will show up in your "Effects" list.
Here's the way that works for me best:
(1) Analyze > Plot Spectrum > set graph to Spectrum, Hanning window, 8192, Log frequency
(2) Slide cursor over graph and find the peak resonant frequency that you want to remove
(3) Effect > Notch Filter
(4) enter Notch Frequency you want to remove, enter "4.0" for the Notch "q" (gives a steep-sided notch, won't affect other frequencies around it)
(5) Analyze > Plot Spectrum > see if what you did was what you expected.
(6) Repeat for any other resonances...
Viva Audacity!