[Acoustom]

Thanks for all your replies. I have a few more things to report. Yes Howard the ball end of the strings are nice and tight against the bridge plate and there have been no humidity changes recently. My guitars are all sitting comfortably at 70 degrees with 42% humidity. I did check the frets with a fret rocker just now and the fifth fret is just a tiny tiny tiny bit higher than the 4th and 6th frets. Could this be the problem even though it's a miniscule amount difference?