I play a MIM Fender Jazz that I recently got defretted. It sounds great but I have noticed that when I play the E and A strings above the twelfth fret, the sound of the notes becomes wobbly and many undesirable overtones are present. I have work extensively on making sure the bass is intonated correctly. Could anyone identify my problem? It has the stock bridge and is strung with D'addario medium gauge flatwounds. Thanks for the help!