Are you talking about strings ringing/making noise even though its not the string you are currently fretting/picking? If so, the solution is to lightly mute the open strings with the heel of your picking hand as you play. This takes practice, but will rapidly become second nature. Also, if you're playing a guitar that uses a trem system, you'll have to be careful that muting doesn't push on the trem sending the guitar out of tune as you play.

You can also use your fingers on your fretting hand to mute strings, but that is more common when playing chords than scales.