First of all, welcome to headfi!! There are a few issues here.
1. You may have a revision 3 driver. If that is the case, then you can mail the hp back and they will repair it and cover the cost of shipping, just save your receipt. Just pull off the earpad and check the color. White=good Sandy Brown=bad
2. Hifiman has been good about standing behind their products. Just email them and I'm certain they will take care of you regardless of the issue.
They have an open announcement thread here that you can use.