Yeah, this one's common. It's usually something loose or an obstruction, not necessarily a motor failure.
First, unplug the unit. Check if the noise is coming from inside or outside. Outside, make sure the purifier is on a stable, level surface and isn't touching a wall or furniture—it needs at least 8 inches of clearance on all sides, especially around the air intake (front) and outlet (side). Vibration against a surface can cause noise.
If it's internal, open the magnetic front cover and remove the filter. Check for any foreign objects (like a piece of plastic, a toy, or a large clump of dust) that might have fallen into the intake. Re-seat the filter firmly, making sure it's not crooked. Snap the cover back on securely.
IF THAT DIDN'T WORK: The motor mount could be loose or there might be internal damage. Also, never run the purifier without a filter installed, as that can cause issues. If the noise persists after checking for obstructions and reseating the filter, the next step is to contact PuroAir support. Don't try to open the unit yourself.
HEADS UP: A constant, low fan hum is normal. A new rattling, buzzing, or grinding noise is not. If you ever smell something burning or hear a loud abnormal sound, unplug the unit immediately and contact support.