I have a shot of someone speaking in an small office and the mic was set near him but not on (Lav would have been ideal). The result was a very slight room echo ambient sound with big time noise. Most likely due to the air conditioning vents. I used noise removal in Audition and it did a fairly good job BUT it left me with wobble/metallic sound when the person is speaking. I read that this does happen but if I easy off too much on the noise reduction it's not enough and if I do it enough I get that wobble/metallic sound effect. Is there a way to flatten out that sound and give a bit of life with out the person sounding like underwater robot? I'm exaggerating but I'm sure you all know what I mean. ;)
Noise reduction in Audition and any other wav editor is limited in it's effectiveness. Minimal usage is always best for maintaining sound quality.
I'd try adjusting EQ levels before using noise reduction. Just EQing out the narrow band where most of the noise is may be enough to make it usable without additional noise reduction.
Another way to reduce noise is Phase Cancellation. You take a recording of the noise and invert the phase and play it bake along with the audio track with the noise can cancel out the noise.
Check out https://forums.creativecow.net/thread/30/862873