I had the same problem with Wheezy on an eeepc, with pretty much the same
aplay output, pulseaudio and all. It turned out to be a configuration problem. This solved it for me:
- Open alsamixer in a terminal
- Choose F6: select sound card. I had two choices: a) default b) HDA Intel. Highlight HDA Intel and press enter
- More configuration options should now be available in alsamixer
- Press the right-arrow key until you find an option named auto-mute
- Enable auto-mute
