I noticed my CPU was maxed out when trying to playback an Ogg Vorbis file I recently created. On a hunch, I tried playing around with the metadata, since I have plenty of Ogg Vorbis files which Rhythmbox never has trouble with, and the title and artist fields seem to be the only things that stuck out about this track.

The title is Amhrán Mhuínse, and the artist is Líadan. When I change the artist name to "Liadan" instead of "Líadan" CPU usage returns to normal ish when playing back the file, ~5%. Yet once I insert that í character back into the artist name, CPU usage maxes out on playback.

I've tried inserting the í character into the artist field on other files... same issue on playback. Also, I noticed both rhythmbox and gvfsd-http were flipping out and maxing out the CPU. I had the Context Pane plugin enabled, so I tried disabling that, and sure enough the problem went away.

Seems like the Context Pane might not be handling non-ASCII characters well in an HTTP request or something? I don't really have the skills to dig much deeper than that, but I have isolated the issue this far: when the í character is in the artist name of a track and the Context Pane is enabled, the CPU maxes out and cycles like crazy upon playback.