Either your saddle is too low, causing the strings to touch the frets higher up on the fretboard, there is a high fret on the fretboard somewhere, or your neck is warped or improperly joined to the body at a bad angle. What is the string travel distance (action) at the 12th fret? does the string travel about 1/8" or more? is so, then it's probably the neck or a high fret. If not, then a low saddle may be the culprit. Sight down the neck from the body end. The frets should be laser line level. If one sticks up, bang it down gently. Try a big rubber eraser and a lightweight hammer. If the neck seems arched when you sight down it, then you got a warped neck. if the neck looks really flat and all the frets are perfectly level, then either your saddle is too low or the neck is joined to the body at a bad angle. Either way, raising the saddle will cure the problem.