So, I emailed them and am waiting for their feedback.
I am also getting this problem with my HE-400, with the right channel stop working sometimes. This one was from a replacement of another HE-400 that had a lesser problem with the right channel.
To make sure is this the revision 3.5 / revision 2?
Will see if test headphone for a while then will contact Hifiman if the problem still exist.
Edited by wredj10 - 10/29/12 at 11:13pm