Re: Problems with screeching sound
Ok. Then, without hearing it, I suspect it may be that you have too much neck relief, combined with low bridge saddles - this may have been what you meant by "intonation", though they're not the same thing.
When the neck has too much relief (bends away from you when you look down at the guitar while playing) to get the overall action low enough, you have to lower the saddles/bridge. When you fret a note at 12 and up in this situation, that part of the neck isn't so far forward, so the strings begin to vibrate against the higher frets, which causes higher pitched resonance (it can sound a little like an auto-tuned sitar).
Try tightening the truss rod by quarter turns, then reset the saddles/bridge so that overall action is as you like it. Play it at the 12th and up. Keep repeating until the high-pitch noises disappear. As you do this, also check that it doesn't begin happening with notes fretted at 1st-5th, which would be an indicator you've gone too far.
Search neck relief/truss rod adjustment on YouTube and you'll find videos.
Sent from my iPad using Tapatalk
