Audio software problem iPhone4, only the right side is working!

I have headset problem on iphone4. When i plug in my headset, the left one its not work, only the right one.. Eventhough i can hear from the right speaker, the sound quality very bad, the noise keep comming out at maximum volume (100%). And when i turned the volume less than 75%, the sound suddenly disappear.. i've got stress with my iphone4.. I think its the software  problem..  I also try used so many other headset, but still same, the left one its not work, only the right one. 

The only way to hear music i using bluetooth headset.. When i using bluetooth headset it works very well, but i must charge my bluetooth headset battery everytime before use that, and also it will drain my phone battery if i always turn on my bluetooth.  ㅠ_ㅠ i've search on google, every iphone forum to solve my problem, but i got nothing.. 

If the problem is the audio jack connector, so why when i turn down my volume less then 75% the sound at the right speaker suddenly disappear? And why the noise keep coming out at the right speaker (volume upto 75%) ? i also upgrade my version from ios 4.3.3 to ios 5.0, but still same... ㅜ_ㅜ i don't want to go to apple service center, because my iphone is already jailbroken..  I wanna try to replace audio jack connector with the new kit, but i think it will useless if the problem is the software.. Right?

Somebody please help me.. I'm sorry if my english bad ^_^v