sometimes NR just doesn't cut it.
if you open the file in the file editor (ie double click to make it full screen)
then switch the view to spectrum instead of frequency (top right above the mini waveform view), you may be able to detect the affected frequencies visually and notch them out with an EQ.
the spectrum view is quite cool and can be tweaked to zoom in to certain frequencies or switch between linear and logarithmic views. once you are in it, right click anywhere in the display to show spectrum controls.
if you do see the hum / buzz you can then make a marquee selection of just those frequencies and then reduce the amplitude of them. (shift cmd L)
or just apply Parametric / graphic / band EQ. pretty much the same thing.