Oh,
that bass! I remember it now, glad you ended up with it, after a little ride on the merry-go-market.
One of a couple things is going on. It's
possible someone filed the E-string nut slot out, but I'd check pretty close to see if the first fret was 'bucked' on the E end. Sometimes, particularly this time of year when it's dry/cold, the ebony contracts just enough to release the fret tang allowing it to spring upward, however slight. Added to that, those super-awesome T-I Jazz Flats are very low tension strings, which if the truss rods have any turns at all on them, might be just enough geometry to get you a little fret rattle. Put a short straight edge on there to check... if the first fret end is a bit high, you'll feel it bump. If so, this isn't a hard fix for a competent repair guy. Sometimes just a quick thump with a (nylon) fret hammer to re-seat the fret. Sometimes a little dab of CA glue in the slot, and clamp the fret in place.
Glad to hear you got some relief with paper shims meantime.
