weird single notes sounding sour problem
My MM Sub 4 has a problem on the higher registers. From about the 14th fret up, when I play a single note, it sounds like a sour chord. Almost as if I were playing a D and then another D note within the same octave, but slightly sharp or flat. I thought it may have been the cheap strings I put on going dead, but it's doing the exact same thing with a brand new set of strings. It's intonated perfectly, and the neck is dead straight. I've heard this on two guitars before, and it went away with fresh strings, so I'm a little worried.
Can anyone offer some insight as to what this could be?
Rickenbacker Club member #483