This problem is most evident when pidgin plays sound effects, but I do not believe it is specific to pidgin because it can be reproduced from the gstreamer command line:

gst-launch filesrc location=/usr/share/sounds/purple/login.wav ! decodebin ! audioconvert ! audioresample ! alsasink

To better describe exactly what I am hearing: this particular audio file contains three short ascending tones. The first tone sounds correct, and plays for about 1/4 second. The second tone has a bit of crackly fuzz at the very beginning, then quickly resolves into the correct sound. The rest of the file plays flawlessly. The crackle is very short (maybe 1/16 of a second), but it is annoyingly obvious.

This problem is not 100% reproducible. About half the time the sound plays normally, and half the time it exhibits the problem. The precise sound of the crackle varies; it makes me think of uninitialized variables. The problem also occurs when playing other audio or video files, not just the one listed above. It also happens when using the osssink (which ends up going through alsa emultaion anyway, I believe). It happens regardless of volume.

If I play the file using "aplay /usr/share/sounds/purple/login.wav" the problem never occurs, which is why I believe this is a gstreamer bug.

I do not have PulseAudio installed.