Using Ubuntu 12.04, 64-bit version, installed on Lenovo X220 laptop. Fresh "default" install and settings configuration.

When the laptop is plugged into a power source, the touchpad's onscreen cursor (the white arrow that shows position) shakes excessively when trying to use the touchpad to control the cursor. The shaking is so bad that it essentially makes the touchpad unusable. For example, trying to click the minimize button in a window's upper left corner will routinely result in accidentally clicking the close button because of the cursor's shaking.

The problem is NOT present when Ubuntu is running on battery. But this means I can never have Ubuntu plugged in and charging while I use it, which is very inconvenient at times.

I'm using the power block and cable that came with the X220. But I also tried using a larger power block and cable that came with another Lenovo model - this power block is approved for use with the X220 and is sold on the Lenovo website as an X220 accessory. But this larger power block did not improve the shaking behavior either.

I have no special settings enabled for the touchpad. But changing the settings has no effect on this shaking behavior either.