Vascular Question - Corotid Artery

I have a question. A couple of years ago I had a corotid angiogram to find out why I hear my heart beat in my left ear 24/7. What the doc told me was that you have one vessel that carries blood to the brain and 2 that carry it out and only one of mine works, and the one that works is on the side where I hear the constant hear beat which means I am just hearing that vessel or artery work harder to carry blood out. Shortly after I lost health insurance and have not yet been able to see a specialist to explain this further. I cannot find anything on the internet as to why mine isn't working. He said it is not blocked (which would be corotid artert disease) as the dye went through it. It just doesnt work. He said it was probably a birth defect, although the pounding in my ear did not start until five years ago. No one was every able to explain what can cause this, what, if anything I need to do about it etc. The doc kind of compared it to only having 1 kidney, as long as the other worked. He made it sound like no big deal. DOes anyone know anything about this condition?