Funny you should ask.  My left ear has constant ringing and it just started lately.  I have to wear ear plugs at work and I was wondering if that had anything to do with it since it seemed to start up after using the ear plugs for a while.  I do listen to my ipod a couple hours a day while I walk but I usually keep it on low. I had my ears tested at work and failed the ear test so got them re-tested and I did alright although my hearing is not as good as it was a few years ago.  It really drives me crazy sometimes.