sounds like a bearing. Should be replaceable if you can get those stripped screws out. You might need to drill out the head and use vise grips to extract the screw. it also helps to heat up the screws with a soldering iron to loosen the locktite they use during assembly. If it’s not a bearing, then it may be a loose piece of magnet, in which case you’re screwed and need a new motor.
Thanks Jesse… I will try to dismount the screws with patience and see how it is inside. I am afraid that it might not be a bearing since the sound does not change with the speed. Cheers