Sounds like a door latch/window motor to me , Ive seen and replaced many of them for this reason. The regulator usually show symptoms of cracking sounds or no movement at all when it decides to go bad. I have a driver side window motor for sale if you wanted to try it..plus the motor is pretty easy to install as well..

 

I first replaced the window regulator. This didn't fix the problem. I then got a new passenger’s side door locking mechanism. The problem was that Pelican parts send me the wrong one. It was installed but the car would not lock. We thought the part was faulty but when looking at the part number (8N1-837-015-C) this seemed to be the drivers side door. I have since go a new one via Dan at Vivid when I was last in the US a few weeks back but have not had the time to install it. The window will drop fully when I pull on the interior or exterior door latch abouth 25% of the time.