I did a quick search on the forums for Sansa Clip+ bad sound and I didn't seen anything up front that seemed like it was like the issue I ran into.
For the past Month or Two I've been running Rockbox on my Sandisk Sansa Clip+ 8 gig. I was very pleased with the sound! I printed the entire rockbox manual and looked through all the settings and decided on each setting what I liked. Everything was going well for me, and then all of a sudden I couldn't hardly get any sound out of the player. I booted into the OEM firmware and tried to play a song that way and noticed the same issue there too. I took the card that was holding my music out and put it in an older Clip+ and tried playing a song and it sounded like it should. Then I tried to reset everything on the player, both Rockbox and the OEM back to the default settings and still no improvement. I hooked the player up to a Windows 7 PC and used checkdisk to test the onboard memory and the music card. It said everything was fine. I used the Rockbox software to uninstall Rockbox, and then I used the OEM software/driver that works with Windows 7 to re install the OEM firmware. Again I tried to play a song and the sound was still bad. Next I tried to reformat the main memory. Then I loaded a song onto it and tried again. Still sounded bad.
I'm not putting blame on anything. But I'm curious... Because it seemed like the Rockbox software was able to make my player louder than the original OEM. I got used to running my player at full volume under the OEM while it was attached to some Ihome speakers. When I was running it with Rockbox I ran it close to wide open. I think it was between 30 and 40 on the volume control. I just wonder if it's possible that rockbox over drove the internal amp to the point where it finally died?