Researchers from Ben-Gurion University have developed a new way to steal data from air-gapped computers without network, the Internet, Bluetooth, speakers, or any electronic device connected to it. They used malware to manipulate the movements of the actuator in very specific way to generate acoustic noise that they interpreted into binary data using a smartphone app from six feets away, at a speed of 180 bits per minute. This technique is fast enough to transmit a 4,096-bit key within 25 minutes through manipulated sound signals emitted from the hard disk drive.
Source: https://thehackernews.com/2016/08/air-gapped-computer-hacking.html