Recently I switched my Raspberry Pi XBMC build to XBian and last night there was an update for the latest version that fixes audio popping issues. The Raspberry Pi has developed in to a great platform for XBMC especially since the release of XBMC 12 Frodo.
You can get the update by going to the system settings, XBian and selecting Updates.
Details from the XBian blog:
New firmware fixes “audio popping” (Alpha 5 only)
We just released a new Raspberry Pi firmware for XBian. To get it from within XBMC go to
System -> Settings -> XBian -> Updates. You can do the same from SSH xbian-config -> Updates.
If you for any reason find any problem to updates there is also an manual option to force the firmware update from within SSH and exiting xbian-config.
Than just type those two lines
sudo apt-get update
sudo apt-get install xbian-package-firmware