Either you have a bad pair or you're not getting a good seal. They have really nice and deep bass. They're not very hard to drive so that shouldn't be the problem. The distortion makes me worried though. Also try playing around with different tips, I find them to be very sensitive to different tips/fit.
Volume was not even that high either. I will do some more experimenting when I get home. If they continue to distort would you say they are a bad set?