It is the window regulator. When you pull it out you will see the "teeth" on the regulator "rack" gear ground down at the ends. The thump - thump sound is the pinion gear on the window drive motor turning against those teeth on the regulator "rack" when it reaches the top. In addition, there was some distortion which, I figure exacerbated the condition. The rear ones in my 300D have been making the noise since I purchased it and that is what I found when I disassembles it one day. The regulators are close to $100/each. I will replace them when the windows will not close anymore, otherwise I just release the button when they are closed.

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Jim