Case: But can they hear it?

According to the Windows User Interface Technical Articles, any sounds that play that can be turned off (or if the device is used in a noisy environment which leads to the sounds not being heard) should be accompanied by a message.

Our system meets this criteria as now that we have added the 'beeping' sound for when the device is scanning a word, the screen also displays the message 'Scanning'. This is all information regarding the practical aspects of human-computer interaction.

The post from the Microsoft Website can be found here.