i have this problem quite a bit, except userally its the left messed up mine happens because of too much use i assume ^^; lol too much music for too long
im not sure if there is a way to get it fixed some times messing with the cord,having it a certian(sp) position or something makes it sound ok-er then it was, sometimes works for me til i get too pissed off and want to throw them -.- but eh
only solution id say is go out and get new ones thats what i do when i have the cash and im in need of it

Is there warranty? I guess you could bring it back to the retail store and they'll figure out what's wrong with it.

When mine or my family's headphones break I send them to fixheadphones dot co dot uk

I've had this happen, and it was the cord being bent back and forth too much either next to the plug or where it connects to the actual earphones. Like the wire frays from too much bending, kinda like how you can bend a paper clip so much it breaks apart where it flexes.
If you have a warranty, get them repaired, but if not, sorry mate. Time for new ones.

yes it happens with all of my headphones, it just sucks... and sometimes they both get very low sound