<p>On my Ender 3 v2 printer I recently and consistently get some knocking.
This happens in only two scenarios.</p>
<p>First, it now occurs all the time when printing the initial test strip gets near the top (high Y value), and knocks several times.</p>
<p>Secondly, it occurs if the model (sliced with Cura) has a high Y value (eg: if the model occupies most of the bed).
(If there is room and I move the model - in Cura - closer to the front there is no knocking.)
On the first 10 (or so) layers the printer sometimes knocks when a high Y value is reached and the entire model is thereafter shifted to the front by a few millimeters.</p>
<p>There is a third scenario. At the end of a print the print head is in the middle of the bed and moves up 20 mm then travels directly to the top left corner. At this corner there are 4 or 5 &quot;knocks&quot; (and the nozzle is 20 mm above the bed).</p>
<p>Any suggestions to diagnose/fix this problem will be much appreciated.</p>

[{'answer_id': 19757, 'author': '0scar', 'author_id': 5740, 'author_profile': 'https://3dprinting.stackexchange.com/users/5740', 'pm_score': 0, 'selected': False, 'text': '<p>Your bed has become unleveled or skewed in Y direction.</p>\n<p>When the nozzle is closer to the bed the extruder has to push harder to get the same filament flow through a smaller space, the stresses the extruder to a point that the stepper skips or grinds the filament. This is generally described as a knocking sound.</p>\n<p>You need to find out why the bed is higher at the upper end of the Y range and fix this. Otherwise your bed has become warped and may need to be replaced. There are alternatives in using a sensor (e.g. a BLTouch) to sense the shape of the print surface, it will then automatically adjust for the shape during the first 10\xa0mm (default value) of your print product. Installing a sensor requires new or alternative firmware.</p>\n'}, {'answer_id': 19793, 'author': 'Lewis Baxter', 'author_id': 35023, 'author_profile': 'https://3dprinting.stackexchange.com/users/35023', 'pm_score': 3, 'selected': True, 'text': '<p>Embarassingly, I discovered that the cable to the heatbed was sometimes caught between the on/off switch and the adjacent power plug. So, for high Y values the cable was very tight and the bed could not be moved. Presumably the &quot;knocking&quot; came from the Y-axis motor. The problem was fixed by attaching this cable to the adjacent hotend/X axis motor cable.</p>\n<p>Hopefully this will be helpful to others who have a similar problem. Please add a comment if you experienced this.</p>\n'}]
['https://3dprinting.stackexchange.com/questions/19756', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/35023/']