http://www.ultrasone.com/index.php/en/company/distributors-north-amerika.html   I called the number on that page and got an RMA number.

Hi All,   I purchased a pair of PRO900 headphones earlier this year.  They have been great, and I use them every day at work.  Just two weeks ago, I had the left driver go out on me.  I have no clue as to why this would happen.  I put them down for a little while, then I came back and the...