I am having a similar issue. I am recording raw vocals being captured on my computer with WavePad. The audio is pretty good except for some background noise. So to remove the low-level hum noise I do the "Noise Reduction" by grabbing a sample of the noise, and then doing a Spectral Subtraction.
It removed the background noise near-perfectly, except that now there are times my vocals have a weird echo-like sound to them. Almost as though I recorded inside a tunnel or something. I know this is being caused by the Noise Reduction function, as the vocals before that was fine.
