Random thought...
Ive had my RE-400's for about a year now and i recently had to RMA because the cable snapped inside and the right earpiece wasnt getting any audio unless you fiddled around with the cable.
I contacted HiFiMan and they agreed to RMA, Unfortunately they refused to pay for postage when I asked as i had read in a few other forums that they had done this for other people (mainly from the US i guess) no biggie anyway, sending bubblewrapped RE-400's without the case in a jiffy bag in hong kong doesnt exactly cost millions so i wasnt too fussed about that.
Turn around time was about 2-3weeks which is expected as things can take around 2 weeks to get delivered from Hong Kong. Receiving back a fresh set of RE-400s my initial impression was that they sound nothing like the ones i had sent back and i was almost about to write an angry email asking if they had sent me back a possibly counterfeit product as they really sounded like shit, bass was a little distorted, highs were quite harsh. But i gave the headphones a few days burn-in time and they seemed to come to life again.