Stop Terminal from Making Irritating Noise
From Terminal.app's preferences (Terminal menu -> Preferences), go to the "Profile" tab in the top pane, make sure your profile is selected, then click the "Advanced" tab in the right-hand pane. Under the section "Bell" there's an option for "Audible bell" which you should deselect. There's also an option for "Visible bell", which is a very useful alternative.