I find the default sound for the 'Break ignore' sound event very annoying so I disabled it via the User Interface > Sounds tab in the Options dialog. All is good and peaceful for a while but sometime later I get shocked out of my skin by the noise of an compressed air horn. I go back to the Options dialog and find the sound has become enabled without my intervention. I've even tried deleting the break-ignored.wav from the Program Files directory, yet after a period of time it comes back! I hope this is a bug and not a feature.