I've got a fretless 6 string bass and as of late, I have noticed that on almost exclusively the A string (and mostly the 5th fret and higher) it sounds like what I am hearing is fret buzz although I wasn't aware that was possible on a fretless bass. I am unsure if it is fret buzz due to a set up issue or if they are true dead spots. I don't know if they are are dead spots though because the sustain doesn't necessarily die out on these areas, but i do get some audible buzzing that makes it through the amp when I play, especially on the higher frets. I should note that I have had this bass about 2 years, and haven't really had to have it set up because I haven't experience any issues. I have never changed the strings (because i haven't wanted to shell out the money for them) though because my playing habits fluctuate with this bass. Could the strings be dead and causing the buzzing problems or is it more likely an issue with the fretboard/bass itself? I've got stock Carvin stainless steels on it right now.