In Audacity you can easily add a dehum filter
I just found this nifty nyquist plugin within the audacity forum to wipe out 50 or 60 hz frequencies including most of it's harmonics. Just paste the snipplet below into a text editor and save it as dehum.ny and then place it within the nyquist folder within the Audacity installation. You'll find it then within the effects menu of Audacity:
;nyquist plug-in
;version 1
;type process
;name "50/60Hz dehummer 2.0"
;action "Removing Hum harmonics, ( this may take some time ) ..."
;info: Unintentional reverb effect. Gibbs ringing on transients.
;info: if you find a cure for the reverb please email me: uvw111-reverb@yahoo.co.uk
;control choice "Select mains frequency" int "0=50Hz (UK) 1=60Hz (USA) 2=choice" 0 0 2
;control bfreq "Base frequency" real " 10-10000 Hz " 50.0 10.0 10000.0
;control a "Amount of hum removed" real " 1-100 base Q=(100/a)^2" 15 1 100
;control v "Anti-reverberation setting" real "1-100 " 25 1 100
;control frac "Fraction of spectr" real " 0.01 to 1 " 1.0 .01 1.0
(setf freq (cond ((= choice 0) 50.0) ((= choice 1) 60.0) ((= choice 2) bfreq)))
(setq que (/ 10000.0 (* a a)))
(setq anti (/ 10000.0 (* v v)))
(setq mysound s)
(setq r *sound-srate*)
(setq itern (truncate (* (/ (/ r freq) 4) 2)))
(setq d (/ (float itern) anti))
(setq iter (truncate (* (float itern) frac)))
(defun dehum (mysound freq iter)
(dotimes (i iter mysound )
(setf mysound (notch2 mysound (* freq (1+ i)) (* que (1+ (/ i d)))))))
(if (arrayp s)
(vector (dehum (aref s 0) freq iter)
(dehum (aref s 1) freq iter))
(dehum s freq iter))