In certain situations, an intermittent, high-frequency buzzing noise may be heard from the system. It appears to change with processor activity and can increase in frequency if USB devices are attached.
This buzzing noise is apparent to some degree on all laptops but is perceived as abnormal because it is different from the other more familiar noises the computer makes.
The noise has been isolated to the processor’s power circuit and is only audible when the processor is in C3 (clock-stopped) power state. In this state, the computer is in a low-power mode designed to reduce chassis heat and extend the battery life. The changes to the components in the processor's power circuit are caused by a phenomenon referred to as the Piezoelectric Effect
. When a specific voltage is applied to these components, they begin to resonate producing sounds that fall within the range of human hearing (15 – 20 KHz).
The noise is normal and within the acoustic specifications of the computer.
Replacing parts do not end the buzzing. However, in the event the buzzing is annoying, there is a workaround that can be performed, preventing the computer from entering the C3 state, thus, minimizing the noise.
Enable Bus Mastering Devices to Prevent the Processor From Entering C3 Power State
Enable bus mastering devices, such as the onboard Bluetooth radio, to prevent the processor from entering the C3 power state. This prevents the intermittent, high-frequency buzzing noise from occurring. However, when the system is running on battery only, the battery's operational time is reduced.
To enable the Bluetooth radio:
- Right-click the Bluetooth icon in the system tray.
- When the Bluetooth Settings menu appears, left-click Power On if it is displayed in the menu. If Power Off is displayed, the Bluetooth radio is already enabled.