Karmic sound: speaker's fine, headset's monstrous

[Fajar Priyanto]

Hi all,
I'm on Karmic fully updated on Lenovo T61. I have strange issue with the sound.
If I play any music, from the speaker it's fine, but if I use headset,
the musical instrument is fine too, but the singer sounds terrible.
It's like those if we play cassette with slower speed, almost sounds
like monstrous.
Not sure if it's only me. Thank you.