I was playing my Custom GS last night and noticed a strange rattle when I played a B on the A string 14th fret but nowhere else.
It sounded like it was coming from the bridge and since it was due a new set of strings I changed them to no avail.
Anyway after a lot of messing about I found the problem to be the battery contact springs because I didn't have a battery in it!
It seems like it needs a bit of sponge in there to keep pressure on them in future if I'm not plugging it in much.
Craig