Had experienced voice or sound from headset mp4 wasn't good, as is my nature? Sense SE215 owned consumer I give voice "srek-srek". But if using a loudspeaker, mp4 spent a good sound or voice.If you find this problem, you can do what i have done.
1. Try to solder again leg slot headset.
2. If still the same, check the components near headshet slot. May be the leg not glue well. You must solder again. Make sure the component in good position.
3. If the you think component is broken, change with the new one.
Good luck.
