[UnDeadKnight1]

Hi,
I've gotten the Sennheiser HD 439 a while ago (like 3-4 months ago), and I've been using them with the FiiO E17 amp on my laptop and iPhone, everything seems to have worked great, love the sound it produces, nice and clear...until today: the right can sounds muffled, like I'm listening to it through a wall. The problem is only with the right can, while the left one sounds fine.
 
Have I already broke the headphones? (I didn't drop them or anything, just normal use, I use them when hiking). Anything I can do to fix them, or am I better just returning them? (I've lost the warranty card though).

 

[NA Blur]

See if there is hair or something stock under the pad guarding the driver.  You can try to vacuum them out and see if that helps.  Also make sure the connector is fully seated as with many portable devices they will not allow a standard connector to fully seat thus making one or more channels sound muffled or dead.

 

[UnDeadKnight1]

I cleaned the right earpiece and that seems to have done the trick, thanks.
 

 

[NA Blur]

Yay!