Electronic devices such as portable computers may contain circuits that generate radio-frequency noise. The radio-frequency noise may interfere with the operation of sensitive circuitry such as wireless communications circuitry. The circuits that generate the radio-frequency noise may include differential signal drivers that drive signals onto communications lines such as lines in a bus or output interface. A control circuit may power the drivers at an adjustable driver voltage bias level. The amount of noise that is generated by the drivers may vary as a function of the voltage bias level and may produce different amounts of noise at different wireless frequencies. Computer lid position and other factors may also influence the amount of interference that is generated. The control circuit may determine the current operating state of the device and may make voltage bias level adjustments that minimize interference between the drivers and the wireless circuitry.