It's definitely electrical. If I continue to hold the button in the down position after the window has bottomed out you can hear clicking in the same rhythm as when the window came down.

We have a 2001 v70 with a unique drivers door window issue. When lowering the window it pulsates down all the way to the bottom. No problem returning to the top position. It acts as if the power is being delivered to the motor intermittently. All other window controls on the main module work fine......