DIAGNOSIS Yeah, this one's common. The most likely culprit is a rock or a very hard, un-roasted coffee bean (known as a "quaker") that's gotten wedged in the burrs. The Impress's auto-dosing grinder is powerful but can't handle foreign debris.
FIX First, turn the machine off. Empty all beans from the hopper. Use the provided brush to clear any debris from the top of the burrs. Then, you'll need to manually adjust the grind size dial to its coarsest setting (turn it all the way counter-clockwise) and run the grinder for a few seconds to try to dislodge the object. If the noise stops, run it without beans to clear any fragments, then readjust your grind.
IF THAT DIDN'T WORK If the noise persists, the burrs themselves might be damaged or misaligned from the impact. This requires disassembly, which isn't user-serviceable. You'll likely need to contact Breville support for a repair.
HEADS UP Always visually check your beans before pouring them into the hopper. A single small stone can cause this.