DIAGNOSIS Yeah, this one's common. That's almost always something (like a small toy, a chunk of pet hair, or a big piece of dust) that got past the filters and is now hitting the fan blades inside the loop amplifier.
FIX Turn the machine off and unplug it. Remove the main HEPA/carbon filter assembly by pressing the button on top of the unit and pulling it straight out. Look down into the cavity where the filter was. Use a flashlight and a long, thin, non-metallic tool (like a plastic chopstick) to gently feel around the fan opening at the bottom for any obstructions. Carefully remove any debris you find. Reinstall the filter, plug it in, and test.
IF THAT DIDN'T WORK The noise could be coming from the motorized oscillation mechanism in the base. If the sound is a lower-pitched grind that happens mostly when it's swinging side-to-side, that's your culprit. You'll need to contact Dyson support.
HEADS UP Do NOT use compressed air to try and blast the debris out, as you can damage the delicate fan balance or push the object in further.