LS2007

I'm a college student and I record some of my lectures on a high quality DVR (mono 16bit 44K rate). There is a lot of ambient background noise (somewhat like a dull roar sound) which I have been able to clean up most of using WavePad's "Grab noise sample from selected area" and "Apply spectral subtraction based on noise sample" (v3.05). Unfortunately the subtraction process (sample based or automatic) seems to create a very annoying sound left behind that sounds a lot like the gurgling / bubbling of a small fishtank. Any idea what this is and more importantly how to eliminate it? I tried doing a second grab/subtraction pass but no help there.