i have nearly the same problem, my right earphone start, after 2 months of extensive using, with strange noises.
And it doesn't help to rotate the plug in the Ipod.
I think it is maybe a problem with the membran because it happen only if i listen to loud music and only if there is a drum or deep sound. And i have now change my Ipod earphones two times in a ipod shop and the strange noises start after 2 months again.
PS: sorry for my bad english