You’ll probably find its a bearing somewhere that has become dry or is failing, don’t try spraying with WD40 as this just evaporates, i find a spray grease (silicone type) to be better. Or replace the bearings..
The fault is caused by the internal motor cooling fan, the plastic one, inside the motor. It has broken away and is making a real racket.
Unfortunately I havn’t got any other details other than model 620.
I doubt that this fan is available as a spare so it would need a complete motor. I dread to ask, does anyone know the part number and the price of same. 🙂