The moving air sound is fine, but the higher pitch sounds to me like a bad bearing, possibly dry not greased properly. We can't be certain when the fan was manufactured and the type of grease used and if it hardened due to temperature, humidity, etc. This sound is typical of a tired bearing, that needs a bit of grease... but once it starts making that noise, it is too late... the bearing is worn already, and you can only temporarily cure the sound by grease, prity soon it will be dry again. Some cheap fans make that sound from the start no matter what.