You may be associating the sound of guitar to the events of your past where you've whether consciously or subconsciously heard it, something bad happened (could even be tied to watching a movie and certain characters growing onto you, doesn't have to be tied necessarily to you), and thus the mind draws the negative conclusion to it as a mean to protect itself.

The other possibility has nothing to do with your past, but that you do simply find hearing certain frequencies nearly unbearable. That you could also test with other things, right?
If you hate those guitars, perhaps you'd also hate different vibrations with the same or nearly same frequencies..?