Have you ruled out dehydration? It's easy to get dehydrated on a fast day (due to missing out on the water content of food) and I believe it can cause this very annoying symptom. (NB I am not medically qualified).
Ears ring while fasting I found your post looking for information on this very topic as ringing happens to me too. I fast Tues. and Thurs. as part of my paleo diet to fight autoimmune symptoms. It's working great except for the increase in my ears ringing. They ring anyway, but much worse when fasting. All other symptoms, and there were many (symptoms of MS, lupus, Crohns etc.) are 95% gone, but the ringing is worse after about 24 hours at fast. Does anyone know about this or have experience with it? I am in otherwise excellent physical condition, no high blood pressure, fit and active, 6 ft, 180 lbs. I am male, 47, suffered autoimmune symptoms for about 5 years after getting dengue fever. No doctors could help me. Started paleo style diet and now incorporating fasting. Thanks in advance.