One touch windows

[barzya8]

Hi Guys,
Looking for some help with my one touch window operation.
The drivers side window goes up & down when you hold the button.
There is a slight knock when it goes down and again when you raise it.
The one touch does not work on this window.
The remaining other three windows all work as they should with the one touch feature.
My question is, would the window motor cause this or would it be a faulty window mechanism in the drivers door, hence the slight knock.

Another point worth mentioning is the fact that the total window closure/opening feature on the remote control works on all other windows except the drivers door.
Any help much appreciated
David