My Mac keeps playing a sound every now and then

After I updated to OS X Yosemite, I have noticed that I keep hearing a sort of 'chime' sound every now and then, randomly. I don't know what it is, and it seems to happen often when I'm watching YouTube.

Please help if you have any idea why this is happening, and how I can fix it – It's very annoying!

Solution 1:

If someone comes here with the same problem: for me it was the Calendar app. I disabled notifications for the calendar in the notification pref because I am using Fantastical for that. It must have been desperately trying to show me an event and beeped because of that. My solution was also to disable audio notifications and voila, the basso beep disappeared.