Steam keeps making my computer chime!

[Salted11]

Steam has recently started causing system sounds to chime every five or so seconds (that Windows "bee-boo" sound). The probem goes aay when I exit Steam. I opted for Big Picture beta but I cannot get rid of it to see if that is what is wrong. Uninstalled Steam client and reinstalled, and Big Picture was there again like a herpe (yes, I opted out of the beta in Settings). What is Steam accessing that is continuously setting off my computer? Also, this is causing split second lags in all games when there wasnt any before! Argh

[V2Blast]

So if it's a Windows sound: What Fred said.

If it's the sound Steam makes when you try to click on a Steam window, but it will only let you focus on one popup window (e.g. the "verifying content cache" window): uh... Close said popup window?

[DarkCrystalMethod]

Perhaps one or both of your steam friends is sending you a private message.
I would have also suspected you were getting event and announcement popups from the steam groups you have joined, but you don't seem to have any.