I hear a rushing sound and feel a sensation of fluid in the back of neck going to the base of my head sometimes for years please tell me what this is?

No worries: I have heard this phenomenon described by many patients. It is nothing to worry about. I believe it to be coming from movement of the neck joints. These include joints between the skull and the first neck bone called the atlas, and a pair of facet joints at every disc level below that. That's a lot of joints that move, potentially resulting in a sound or fluid sensation.