Here is the quick walk-through I promised:
- Select a few seconds of noise
- Open DeNoise and click Learn
- Click the menu arrow next to Presets, select Add Preset, type in a name and close DeNoise
- Select a few seconds of wanted dialogue, re-open DeNoise and select your preset
- Select the Simple tab - this should be fine for your source material
- Select Algorithm D - provides best results 99% of the time
- Set NR to 10, Smoothing to 7, click Preview and listen
- If you hear artifacts, set the smoothing up a bit and Preview again
- Select Output Noise Only and Preview to ensure you are not losing dialogue
- DEselect Output Noise Only and close DeNoise (NB Don't forget this step!)
- Select the whole file, open DeNoise and click Process
Repeat the above process until you are happy with the results.
This is pretty much the standard NR process for broadband noise, although I have biased it a bit to suit your source material. The Advanced tab gives you a lot more control over your noise profile in terms of the type of noise you are targeting and the manner in which artifacts are handled. You can usually obtain better results, but it takes substantially longer.
The noise in your recording is mainly broadband, but there appears to be a tonal element to it as well, so you would probably link them in the Advanced tab anyway. The real secret to successful NR is multiple incremental passes using smaller (8-10dB) values. Yes, higher values will mean more noise reduction, but will also introduce noticeable artifacts. Also, just in case it is not clear, you must either overwrite your existing preset or add a new one for EVERY subsequent pass.
Your source material will also benefit from higher Global and Fine Smoothing in order to minimise any possible pumping effect from the noise reduction, so once again the benefits of dealing with them separately will be negligible.
Finally, there is often a tendency to want to remove too much noise. Only remove what you have to and no more, otherwise your recording will start to sound artificial. Sometimes I even add in a bit of white noise afterwards to make it sound more natural.
Hope this helps!