My x20 distorts sound and med frequencies are almost gone.

I noticed one morning that my x20 suddenly distorts sound BUT only through the earphones... the built-in speakers give proper sound, and i don't know what's wrong with it. I'm saying it was sudden because i used it the night before, shut it off normally, went to sleep, woke up and it was acting like i said. I'd take it to the service since i have 1 year warranty but i already could not restrain myself from opening it up myself. however there were no "warranty void" labels or anything in sight so legally i should be given benefit of doubt :p
Still i'm afraid they'll say it's a physical problem although i did not touch any pieces inside, just merely looked for suspicious dangling wires or such.