DIAGNOSIS: That's the vibration pump cavitating—it's trying to pull water but can't get a consistent flow. Usually means a low water level, a clog in the intake tube, or the machine is fighting an airlock.
FIX: Immediately turn the machine off to protect the pump. Fill the water tank to the MAX line. Check the small silicone intake tube at the bottom of the tank compartment; make sure it's attached and not kinked. Turn the machine back on, and with the portafilter removed, run the brew switch for 10-15 seconds to try and clear any air.
IF THAT DIDN'T WORK: There might be scale or debris clogging the internal water path from the tank. You'll need to run a descaling cycle, making sure the descaling solution gets pulled through the pump.
HEADS UP: Letting the pump grind like that for more than a few seconds can burn it out. If the noise persists after checking water flow, the pump itself may be failing and needs replacement.