There really isn't anyway to actually remove noise from inside the sample. Even EQ-ing a sample or gating the noise will not get you very far if the actual noise is in the important part of the sample, aka the voice. You can EQ but if you edit the frequencies too much, too little, or incorrectly, again it wont get you anywhere. It may make a slight improvement, but not by much.
The only true way to get rid of the noise and make improvement for the bank is to re-record and eliminate noise before hand. Such as recording in a less noisy environment, changing your microphone or trying to change the quality/settings of your current one ect.
Things like EQ-ing or using audacity(which really wont help) could actually affect the sample where you didn't want it to as well. For example, consonants are basically noise-white noise-no tonal frequency sounds and if you cut those out by just trying to eliminate noise, your samples will basically be all vowels, or just really weak consonants which doesn't go well in utau.
If you need help/have more questions you're free to pm me T u T9 I've been in the mood//smacked