I've also been experiencing this. After the Ultimaker heats up and releases the initial puddle of material at (0,0), it moves to the center of the table to begin the part and grinds really loudly as it does so. The noise also goes away once the part starts to print. We think it might be related to the fact that we're at the end of the spool of material and the bend in it might cause it to pull, as we just ran a new spool and didn't get the grinding sound, but we aren't sure. Anyone else have ideas on what the issue might be?