I don't know Audacity really - I only know Logic, Garageband and Cubase.

Audacity's noise reduction filter is basically EQing of a sort, those it sounds like it's a bit of a blunt instrument.

I'm looking at this webpage now:

http://www.guidesandtutorials.com/audacity-effects2.html

Read the bit about equalization and clicking on lines. It's not quite as precise as you get in Logic, but it looks like you should be able to eventually draw a line that will single out the frequency you want to get rid of.