What is “Strat-itis”?
“Strat-itis” is often caused when the height of the pickup is adjusted close to the strings and dissonant overtones are heard as you play further up the frets. It is really noticeable as you play on the bass strings way up the fingerboard. The overtones are due to each pickup having the same polarity (3 South or 3 North Polarity). The string acts like a keeper but is magnetized in three locations. As the magnetic field from the center pickup travels down the string, the magnetic field is repelled by the two outside pickups. As the like poles repel each other down the string, the overtones become very distorted sound wise.
The Strat-itis can be reduced by lowering the pickups on the bass side of the pickups. Also reversing the magnetic polarity in the center pickup will help reduce magnetic repulsion in the string. The notes will have a clearer sound as you play up the frets. The string can have several magnetic fields that react with the pickup’s magnetic field.