Check that the fan blade is fully secure, sometime over time the tags on the rear wear down so blade could wobble, use a 15mm thin wall socket on the front nut and turn the blade anti-clock wise to make sure it's completely tight, you can even then drill a 3mm hole and add a grub screw.
Purple marks where to drill and add self tapper securing screw, if needed ?
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Tags marked with yellow dots.
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