[Ubuntu-BD] sounds come from laptop speaker and headphone simultaneously

[~Split_Fire~]

Dear community,

I'm using Ubuntu 10.10 (maverick) in my Sony Vaio model no: VPCEH"N1E/W.
When I plug in headphone, sound come out from both headphone and also from
the laptop speaker! Any suggestion?

My audio device: 00:1b.0 Audio device: Intel Corporation Cougar Point High
Definition Audio Controller (rev 04)
My alsa version: Advanced Linux Sound Architecture Driver Version 1.0.23.

Upgrading alsa will solve this problem?

Thanks.