The DSi volume button keeps going down.

Take out the SD card from the slot, blow on it, and stick it back in. Then blow in the indention on the volume bar. That worked for me, hope it works for you.

Mine did the same! Have you tried holding down the + button on dsi sound and dragging the volume bar up? If it stays up while you hold that down, then take clear rubber bands and tie them tightly around the dsi on the volume button until they firmly press on the volume button as if a finger was. each time it does it just go to dsi sound and drag the volume bar up with the rubber bands holding down the volume! ^u^ since I've done that for a while, it fixed itself on its own; I guess the dsi's chip gets messed up and thinks that the volume button is pressing on the - button. But there you go, that's how I fixed it! ^u^