Trouble with first print
Hi,
I couldn't find similiar issue. I finished assembling MK3s. XYZ calibration went smoothly, first layer calibration seems to be ok. After that I tried to print deffault model from SD card. And I keep getting this problem with upper wall.
Since it's a standard model from SD card, I assume there's nothing wrong with print settings. And I used PLA attached to the kit. I wonder if it's related to first layer calibration and maybe nozzle is still too high? Or something wrong with assembling? 
RE: Trouble with first print
This seems to be a normal artifact of extrusions without adequate supports. The whistle is known to be problematic, and slowing down the printer is one way to help, but doesn't always work. Others have tried rotating the model to change the cooling air flow from the print fan.
Other than the drooping bridge strands, the whistle looks very clean. I'd be happy with it.