I've recently started playing upright, and my three top strings are fantastic; they have great, full tone. My low E, however, buzzes whenever any note besides the open is played. I've tried adjusting the bridge to as high as it will go, and the buzzing is kind of fixed... but the sound is still SO quiet compared to the three other strings. All four strings are nylon, and noticeably thicker than the strings I've felt on other players' basses. Is this an issue of the string itself, or is the low E just quiet on DB (the instrument's just that way)?