My Danelectro Longhorn Pro has been 100% problem free for years, admittedly mainly as a backup instrument. But all of a sudden the bass now has a distinctive rattle on the open E since a couple of weeks. My first action was to replace the strings as they were old (but not "dead"). This had no effect what so ever. The new strings (EBS Stainless Steel) sound very nice everywhere, except the open E. Fretting an F or higher will sound perfect. 12:th fret E is also flawless. Fretting "behind" the nut (to rise tension and pitch as well as height of the open string) will not cure the rattle. Bending the neck back or forward - as in "relief" - will have a small effect on the rattle but not cure it. I have also replaced the nut but the new one did not cure it. Detuning the bass will still cause the open E string to rattle even if it is now a D or C#. The then new, fretted 41Hz does not rattle so it seems more related to open string than pitch. Tuning to F will reduce the rattle a bit. Fretting first position on the A string (to put pressure on the fret) while playing the E will not cure the rattle. Any ideas? They are all VERY welcome. The only thing I can think of right now is if the first string (unknown brand) had a defective core and that I somehow managed to damage the core in the new string as I cut it to length.