The noise does come out with some processing in the mix, and hides more in busier arrangements.
Here's Gumi V6 from awhile back:
I'd probably tweak a few things in it from later experience, like I wasn't in the habit of toning down the automatically applied pitch drift and vibrato, which also helps. The noise shows up more when those are exaggerated, which V6 tends to do by default. (I just open the inspector and drag the sliders down, and introduce them more minimally.)
I don't recall offhand what sort of effects chain I used on the voice, but I would never let anything out the door without compression, EQ and reverb at least. I would imagine I probably swept the EQ over it to find the buzzier part and made a cut there.
I think what Turbo (of Eurobeat cover fame) did with Gumi V6 was also good. The description didn't specify Vocaloid/SynthV, but there's a Google Drive link in it to the VPR file and a document about the process.