I have a problem with the sound from the headphone jack on my iPhone 3GS. Sound from the speaker is fine, but the sound from the headphone jack (on any headphones) is distorted at normal volumes. If I turn the volume down to about halfway then the distortion vanishes but the volume becomes barely audible.
I've just replaced the headphone jack with a brand new assembly, so it's not a problem with jack itself.
Anyone have any ideas?