First you need to turn off the power, and then remove the cover of the fan to access the fan blades and motor. You are going to need to check for loose screws and tighten them, clean any dust build up with a vacuum or compressed air, and inspect the blades for damage or misalignment. Adjust as needed. If the noise persists, consider lubricating the motor with a silicone spray or replacing the fan if the issue is more severe.