To reproduce this bug:
Use the following /etc/asound.conf:
# Ensures software mixing to be the default
pcm.!default
{
# We pass thru 'plug' plugin first, which resamples all audio to a single
sampling rate
type plug
slave.pcm "dmixer"
}
# Ensures software mixing.
pcm.dmixer
{
type dmix
slave.pcm "hw:0"
}

2. Set the GStreamer default sink to "alsa".

3. Play a DVD with GStreamer.

Result: The sound will have lots of audible clicks in it, as if extra data is
present in the audio stream (data from 5.1 channels, perhaps?).

Curiously, after pausing the video once, and resuming it, the sound becomes normal.