There are a few possibilities for choppy music. The first is the headphone plug. Check that the plug is fully inserted.
If the two (stereo) output signals are shunted together, the headphone amplifier will drop the output. This is to protect the amplifier. Some headphone plugs are a wee bit longer than average. If this is your case, pulling the plug outward slightly, about 1mm, may cure the issue.
Some users have installed a wee O-ring on the plug base to solve this malady, keeping the plug from bottoming out in the jack.
The last choice, if you’re not using VBR encoding, is that the Sansa is running into a huge file allocation table. This problem manifests itself when working with 4GB and larger memory. To cure this, back up your music, and use the Format command on the Sansa. This will optimize the memory and FAT using 32KB allocation clusters.
Once you reload your music, the stutter should be gone.