I just bought a great-condition 1990 Fender Jazz Plus bass here on TB, and the bass plays great except for an issue I'm having with buzz on an open A string: After I received the bass, I thoroughly cleaned it and re-strung it with D'Addario XL Nickel Wounds in 45-65-80-100 gauges. After tuning her up, the A string exhibits a nasty buzz against either the first or second fret (pretty sure it's the first) with anything heavier than a light pluck. The odd thing is if I mute the A string at the headstock with even very light pressure - not even enough pressure to fret the string if it were over the neck - the buzz disappears and the string plays fine. I'm thinking that I've either got a bad string (noticed several small spots of corrosion on the strings when I opened the pack) or the gauge is too light for the nut (bone) and the setup (rather low). The frets are in great shape for a 23-year-old bass, and I know that the bass was set up for its old strings (looked to be Elixir Black Beauties; not sure of the gauges) fairly recently. I'd appreciate any insight into the issue, and suggestions as to what I should try first to eliminate the problem ... ?