I felt the same thing in the months following my concussion and the sound of my heartbeat was also often accompanied by a migraine like head ache.

I donīt exactly know what causes it though. I could imagine the blood pressure in the brain being too high somehow because of a dysfunction in the brains auto regulation system.

I do believe these problems are quite common after a head injury.

If you get a head ache while exercising or the sound of your heartbeat gets worse, it could point to auto regulation problems as the culprit.