Many causes, I lived with it since 2006 after an incident. However I may have listened to it many years before but thought it was normal. It's because of that incident that I've become aware of so many symptoms...
My case, I hear and feel the pulse pressure differences from within my brain case via a hole between my brain and inner ear, (Semicircular Canal Dehiscence). There are many other ear problems that can cause your pulsing, if not the above.
It is called pulsatile tinnitus. You can look it up on the internet. I'm not sure what the causes of it are. Hope this helps.