They break from the nut at a decent angle so it's not rattling there, I've checked everywhere the string touches. Nut, tuning machine, all points on the bridge. Nothing.
hdracer, this could just be a normal thing then. I love the sound of the strings, but this rattle is giving me ulcers.
Jasper, it's being used on a fretless with fairly high action, no fret rattle. And no, not a side effect of mwah, either. The rattle happens when the G is open too. No, it doesn't come through the amp (I don't think so, anyway). As for set up, strings already sit high and I can't adjust relief, this bass has no truss rod. But the neck is about as thick (if not thicker) than DB neck so it doesn't bow at all.
Can you hear the waves? Crashing in the dissonance?