I've recently switched from Empathy to Pidgin as my IM client, but I've noticed the notification sounds Pidgin plays on events like a contact signing in crackle. I've never had such problems with any other sound on Ubuntu, but Pidgin seems to have a problem with my audio setup.
I'm running Ubuntu 10.10.
Thanks for your help.
I had the same problem until I opened Pidgin's sound properties and switch "method" from "auto" to "ALSA". Now it works.