I didn't notice an issue when listening to music or videos on the speaker. My sound quality issues were always in calls, and I had more like an electronic feedback, and squelch sound that came through during calls. My calls are crystal clear now.
Have you played with the equalizer settings? I personally find that mine sounds as good if not better than any phone I have had in the past. I do want to pick up one of the blue tooth speaker boxes to have at the office, or carry on trips.
Second, is the sound quality issue coming via music on your phone or SD card, or just when listening to Pandora, Google Music, or other streaming service?