Noise Reduction of Constant Background Noise

I didn't mean more material - I meant more information about what you are trying to do and have tried already. Have you made any attempt to try this? What software have you used?

It is quite possible to do what you want with Audition's Process-based NR, although it takes a bit of practice to get good results with it. There is basic information here but it doesn't tell you everything you need to know. There's a thread here with a lot more detail about how to go about getting an opimal result.