waves and scraping

printing anything larger than 5cm x 5cm results in these waves accompanied by rubmbling scraping noises.
Obviously the nozzle is touching the print for some reason.

It happens after about 10-20 layers of printing.

Gantry is level and square. (it was not from factory)
p.s. Blue tape because the creativity build plates are very unreliable with sticking the first layer.

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