I get random audio on my iMac os x mavericks

Recently and quite randomly I am getting audio ads with only Safari open and other things running in the background.

I have looked for processes I don't recognize and the ads always stop. but it can be a day or two before I hear it again.

Most of my life people have said that I am crazy - but this is actually real. I don't hear voices - this is coming out of the internal speakers. The only external I have is Bass Jump Subwoofer.

Thanks. I am serious about this - no joke. No harm is being done it just is sort of annoying and there is absolutely no rhyme not reason.