Just to state the obvious, the magnetic sheet is on the bed? The grinding noise is only at the end when it’s pressing down? Not all the time when it’s moving?
It could also be that the bed level sensor is failing. When you put a piece of metal below the bed level sensor, do you see a small red light?
You can see a picture here: A350 Proximity sensor not working? - #10 by xchrisd
If the light doesn’t come on there is a problem with the sensor.