Sheridan

My drivers side window has started to make a clunking noise as it goes up, the noise occurs at the same points every time so I suspect is related to the rotation in the motor.
This started happening on the way home from Brands Hatch on Saturday where the window had been used quite a bit to get info on parking from the 'officials'. If I put the window fully up then down several times the noise fades to nothing as if it is warming up.
Anybody have any ideas, I know it is a minor glitch but it is annoying.