Behringer touts their mixers as being very-low-noise, but that's a load of
hooey when it comes to their headphone outputs at least. Curiously, I've
really only used their mixers for headphone applications, so I don't know
what their line-level outputs sound like.

Short version: Buy Mackie instead.

Nevertheless, there is one Behringer product that I am overall pretty
impressed with: Their noise-reducer. It appears to be an original design
rather than yet another one of their cheap knock-offs of the corresponding
Mackie product. (I don't know of any equivalent Mackie product, but if I
did, I'd buy the Mackie instead.) In short, it's the confluence of a
downward expander with a quickly-sweeping lowpass filter. The downward
expander of course is to knock out noise (noise of any sort) while the
source is effectively silent, and the sweeping lowpass filter to knock out
electronic hiss when the expander is ... "open" for lack of a better word.
It seems to work quite well from what I've seen, even doing a reasonably
unobtrusive job when the source is extremely noisy. By the way, I don't
recommend using its "automatic" setting; you'll get much better results
when you fine-tune it to the particular source.

Obviously of course, any example of this sort of electronic fakery must be
treated as a last resort, and if you do have to resort ot using them,
they'll do a vastly better job when the source is only slightly noisy.
That is, first and foremost, you have to do everything possible to simply
get the noise out of the source before applying noise reducers.