Hi everyone! 
I've been into this hobby for a few months now. I've finely calibrated my printer and haven't had any problems, and the surfaces I print are almost perfect. 
Usually, however, I print objects with small surfaces. For the first time, I decided to print something as large as the entire build plate, and I ran into several problems. First, pillowing in some areas, starting from the lower layers, despite good flow calibration. I temporarily forgot about it because it wasn't a big deal, as the defect is in a hidden area, and proceeded with the second print. 

This time, I noticed that during infill, the nozzle seems to be rubbing along the grids, producing the noise in the video. I've never heard this noise before. The print bed should be level, since I always leave the calibration option enabled. All the axes were greased a few days ago. 
What could it be? 

Thanks for your help!

PS: Even though the plate was perfectly clean (degreased with dish soap, cleaned with IPA, and handled with gloves), I was worried about warping, so I added some glue stick. The distribution wasn't exactly uniform, which made me think the print defects on the white piece were due to an unevenness in the plate caused by the glue itself. 

PPS: White print in comments.


Crackling noise while grid infill printing