I just recently purchased a G&L L-2000 4-string bass, and I am getting fret buzz close to the neck on the e and a string. i have tried to raise the strings at the bridge and it helped some, but it still buzzes especially on the a string usually from the neck all of the way to about the 10th or 11th fret. It also sounds different on the a string just by ordinary plucking of the string. What can I do th fix the problem?