It's possible that chronic inflammation has created this imbalance. That would be a result of past antibiotic use creating a "leaky brain" and ongoing levels of inflammation in the body generating more brain inflammation. The result could amplification of nerve signals to the point that you're hear so much.
Candida can create the ongoing levels of inflammation that continually feed the brain inflammation. Parasites, chemicals, viruses, etc., could also cause increased levels of inflammation in the body that played a role as well.
If you live in the States, I would first try a chiropractic doctor who is well-trained in S.O.T. If that didn't help, I would go to Dr. Carrick at Life University in Georgia. His specialty is the brain and neurology.