This started happening to me in 2006 when I smoked from a poor man's pipe with some friends. I still go through this but once in awhile. It became a concern so I went to the doctor to get my ears checked up and the doctor said it was clear.
I also had this last week but now Im kinda use to it. When I smoke it the ringing got a little worse. Im kinda use to it now.. :wtf: