[linux-audio-user] Cutting background noise from a voice recordering?

Hi folks. Thanks for the round of suggestions about software for cutting up a large .wav into CD-sized pieces - I'll probably be using sox's "trim" option the most. I have a new question though, about cutting background noise from a recording. The conference room my workgroup uses the most, has an incredibly noisy air duct passing right above it, and I'm told there's pretty much no way they can cut the noise output from it, without curtailing the airflow to the remainder of the building. Which means that aside from not being able to hear what's going on in meetings sometimes, especially when people are mumbling (I have a tad of a high frequency hearing loss), it also means that my voice recordings have a more or less steady level of background noise due to that air duct. On top of that, in some of our meetings, people want to use a projector, which adds its own level of white noise - even after we shut it off, since it needs to cool down slowly to minimize thermal stress. Which brings me back to my current question: What sort of linux software might be good for eliminating the noise from a loud air duct and/or projector fan from a voice recording? Thanks!