iPhone 3GS headphone sound is crackly 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?
Gonna say if you take it to Apple, they will confirm the audio processing chip on the mobo has maybe become faulty. Seen this before, took it to Apple, the chip responsible for audio processing had fried itself (not sure how). They replaced my iPhone.