It has been 6 months since I've got my Jackson JS32 Kelly, and today I have noticed that after I fret down the E note on the 12th fret on the high E string, the note's frequency is fluctuating, and it sounds a bit annoying. Do you guys have any advice?
It is possible that something on your guitar resonates near the high-E 12th fret frequency. Springs in the "tremolo" (vibrato) system for instance.
The best way to track something like this down is to put your finger on parts of the guitar while inducing the behavior and see if you can make it stop happening. Some things will be more clear when unamplified; some things you may need to get clever about, such as putting can headphones in contact with the body and play the note frequency on a loop so that the guitar resonates, but you can still hear any induced vibration.