Ultimaker quiet retraction

This greatly reduces the noise from the extruder motor. The wooden backplane of the Ultimaker did act like a drum.

To find out how much noise this upgrade can remove, carefully un-hook the feeder while printing, and hold it in your hand. Answer: it makes a huge difference.

Update1: separate, much better holder for the bowden coupling, and other tweaks.
Update2: upper hook should withstand PLA creep better.