There are different types of noise, with different treatments.
I had incredible results with "Exact Audio Copy", using the noise profile and remove, on several types of sustained noise.
The actual task it handled excellently was removing "hall noise", mostly air conditoner noise, though fortunate in having a really clear noise sample - that type of removal demands a clear sample.
I tested that to the extreme, with some music that I deliberately BURIED in PC fan noise - not kidding, to the unassisted ear, it just wasn't there. The same noise reduction was actaully able to get something back, not great, but if it had been speech, it would have been understandable.
Impulse noise requires a different treatment, clicks and pops need to be individually detected and removed, and this is generally handled quite well by the "LP cleaning" settings on many programs.
A simpler way of dealing with hiss (surface noise or tape hiss) is a lowpass filter, or a filter which varies according to the masking of hiss by programme content, though if you can find a hiss-only sample, the noise profile method may be worth a try.