The truss rod is rattling. The key there is - "loosened the truss rod as much as ......"
Normally you want a little tension there, even if you dont want it to take out any curve caused by string tension.
I've found that, depending on the string gauge, humidity, etc etc, your neck might take a few days to really find its way and begin to curve, at which time you can straighten it a bit, for proper relief. Not sure what gauge strings you're using, but you might want to increase one gauge (say from 9s to 10s) just to help things along for a while.
And.... there's also the possibility you need to level the frets for the lowest action.
You make no mention of the very important numbers - radius, actual measured relief, string elevation above fret 12 for the low and high E's (assuming bridge curvature is set correctly as well).
Lately, I've set up a lot of 12 inch radius fretboard guitars. They seem to like about .010 relief, and 3.5/64 elevation on the high E, 4/64 on the low E. This allows a decent bend up at fret 12-17, where things tend to fret out if they're too low.
I'd like to know those critical numbers for your instrument - along with bridge type, to see if your setup is ok.
And... do you need to scrape the finish from the frets?