After updating to U7, I now get a random looped sound effect. This starts up about 30 - 45 minutes after starting the client. I can make it stop by muting and unmuting (via the audio control panel), but it starts up again in a minute or so. Restarting the client makes it go away for another 30 - 45 minutes; relogging does nothing.
The exact sample that's looping isn't the same every session, although once it's started, it mostly stays the same (i.e. after 40 minutes or so, a sound sample will start looping; from then on, the sample will start looping every minute). I think the sounds are spell casting sounds, but I'm not certain of this.
This is apparently a known issue. The entry in the 'known issues' thread says alt-tabbing to another app makes the problem go away "for a time". I've submitted a bug report and a technical assistance request, so we'll see what comes of that. Having to toggle mute or alt-tab once a minute is making the game pretty much unplayable for me, and completely muting audio isn't really an option either (no voice chat). I'm posting this here so that anyone else with the same problem can speak up.
I'm running under XP, haven't changed anything in settings or hardware (aside from letting U7 download and install), never had this problem before U7.