Hi,
I don't post often but I think there's a lot of reasons why you may be experiencing background noise or static. Like others have stated, the microphone may be the first cause. Use a pop filter, record in a low noise area that will also not produce any reverb into your feedback, ie. an empty room will do this.
Find the sweet spot to your microphone, don't record with very quiet samples - ***This is not to be confused with a quiet bank, but rather your microphone not having recorded your voice fully enough. You can still have a soft bank but recorded fully. An easy way to see is to look at the wav files loaded up, are they tiny and low or full and take up most of the space***- As I noticed when running through utau, you get far more static and bg noise come through. Also, try not to rub, over breathe, or make subtle noises. I often rub my legs while recording and I find that can occasionally be heard.
Make sure your settings are correctly down and you're actually recording with the microphone. Some USB mics, like my blue snowball, can disconnect without you realizing or arent fully connected.
For when it comes to actually putting it through utau, utau will butcher your samples to a nice pulp no matter your quality. Use the right resampler, or resampler combinations, flags, velocity, etc. If you're experiencing static or robotic like noises on longer samples, chances are it's your oto and it indeed can be fixed. I use TIPS as a resampler and the oto and amount of recorded line to work with heavily influences this. Velocity also influences the stretch factor that may contribute to any noise. Experiment with what resamplers work best, I find moresampler to be fluid, but very fuzzy sounding. Lowering the envelopes in utau can also be a way to limit the bg noise. For example, and end breath or note with static at the end - lower the end of the note with the envelope.
Lastly, there is no perfect bank. Many banks may not have as much of some qualities as others, but it really comes down to how it's used in UTAU and mixing. A lot of the sound you hear in the raw samples can be removed while actually mixing, and some static and robotic sounds can be masked with the actual song and mixing. You may think an utau sounds really nice covered by the owner or someone else, but that may change when actually using it.
If you don't want to spend money on utau, its fine, just work with what you got. I've only devoted around 75 dollars to it and there are always ways to deal with issues.
I hope something of that mess was helpful, as I assume that's what you meant! : 'D