How do I remove a loud hum from a (.wmv) file?

I just recorded an interview using Debut Video Capture Software and a store bought mic. The mic is not very good and produced a loud low frequency hum throughout the video. Is there a way to edit a (.wmv) file and clean up the audio, that is not expensive? I tried putting the (.wmv) files through Audacity, and I was able to clean up the hum. I opened up Windows Live Movie Maker. I loaded the (.wmv) file, and then loaded the mp3 file from Audacity. Unfortunately, Windows Live Movie Maker plays the original audio with the hum, along with the mp3 Audacity file. So, the hum was still very audible. Is there any free software that would allow me to easily clean up the (.wmv) file and remove the low hum?