Bad 'grinding' noise at the start of every print

When I start a print my Mendel90 makes a very brief 'grinding' sound (sounds like 'grrrkk') just as the X carriage begins it's descent from homing at the top. It's a split second long but very disconcerting! Happens every time. This is Slic3r 1.2.6 experimental x64. It doesn't happen in version 1.1.7 stable. It also doesn't happen when I slice with a different slicer.

Any ideas what might cause this sound?

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I used to get something like that from the starting gcode "G1 Z5 F5000", where G means move, Z5 is the coordinate, and F5000 means lightspeed. I do not have hyperdrive capable thrusters on my threaded rods, and so, the mundane stepper motor would skip when it attempted F5000. I now have it set to "G1 Z0.35 F100" and I don't have the problem any longer.

This, however, is a superficial solution, and I should really go into the firmware and change the max speed for my axes.

Perhaps try diving into your gcode and change all the F values which are before the X carriage descent and see whether that changes your problem.

In the expert mode of Slic3r you have the option to change the start gcode.

It's funny. The machine is not exhibiting this behavior now. It suddenly just stopped and I haven't felt like testing other versions of Slic3r or other slicers to try to repeat the problem. 1.2.6 us working very well. So when I have more time I will test other slicers but for now all is good.

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