Headphone Issues?

I have been experiencing issues with headphone playback on my iBook G4 for at least several months now. The specific issue I am having is that whenever sound is playing out of one sound channel (left-side only or right-side only) it sounds perfectly fine (it is monaural though). However, as soon as both channels are turned on, the sound becomes extremely distorted, sounding the worst when it's perfectly balanced panning-wise.

This issue seems to occur throughout all of the programs, so it's not specific to a single program. The sound outputs normally through the system speakers, and the headphones I use are in perfectly useable condition, so I'm under the impression that it may be a hardware-related issue, specifically in terms of the headphone jack, but I'm not 100% sure.

Any ideas as to what might be causing this problem (and any suggested solutions as well) ? 😕