Treble's gone when headphones are in and balance is equal.

When I plug my headphones into my computer, all the sounds I hear have a extremely (almost inaudible) low treble. It's strange because when I change the balance of volume to either side, the sound comes out just fine.

When listening to the bare speakers, the sound is fine, no matter the balance.

It kind of seems like it's a headphone problem, but I'd like to make sure before I go replace it.

 

Have you got a stereo/mp3 player to test the phones out?