[SonicVanguard]

If you're talking about background noise that's occuring simultaniously with audio that's important to your final product there's very little you can do. You can try various filtering techniques like notch filtering but it's a difficult technique to do correctly without adversely affecting important aspects of your audio.

I'm not sure if a package as limited as Sound Forge Audio Studio is really capable of critical editing techniques like that. Please don't take that wrong - it's a good product, but there are very few prosumer products that can handle editing like that and Sound Forge Audio Studio is a crippled version of a prosumer product (Sound Forge 8).