I bought a used FiiO E10 from ebay and got a few problems with it.
First off, music and game playback is good and sounds great, no problem with that. However, when the audio playback ends or is ended by me, there's a crackling noise in my left ear cup. It doesn't happen with my Xonar DGX nor with my Realtek onboard sound.
The other problem is, that the E10 seems to have problems with Windows sounds. For instance, the sound that comes when you click the volume button in windows (screenshot: http://imgur.com/NDmQGVZ), is distorted, especially when you click fast. With my Xonar DGX and the Realtek onboard, I can hear this without distortion.
Also, the sound when you click folders is simply not played. You can hear it here at 0:28 http://www.youtube.com/watch?v=eGGI1YQV9FI
What I've tried already:
Tried different USB ports
Tried different PCs
Tried different headphones
Tampering with the sample rate
Is the unit faulty?