Just traded for a bone stock Gibson Firebird....but I'm having issues with fret buzz. I've gone through the entire thing, string height, truss rod, inotation, and pickup height. Even raised the string height a little more.....still get fret buzz.......on almost all the strings, most of the fret board, mostly the low E. The catch is you can't hear it when playing through an amp. What could this be? stock gibson nut? low action?