I am trying to play pizzicato melodic passages with a consistently full sustaining and beautiful or bouncy, joyfully swinging tone and, occasionally, I hit the string. which produces an unpleasant, metallic sound, as you get when you slap the string intentionally. I rarely have the problem on the two highest strings, but more often on the two lowest strings. Do I need to change the angle of my fingers pulling the string? Should I raise the height of the strings? What do you suggest?