If you're playing a single one note groove, the secret to playing it completely crisp and clean is to use your pinky on the left hand to fret. Even if it's a little awkward, the difference is huge. The reason for this is that it allows you to rest all other fingers on the string while playing, and as soon as the pinky lifts up, the note is instantly muted with zero harmonics. I find when I try to do this with my index, there's a little bit of harmonics or other noise for a short bit. Try it!