I am fairly certain that this is not a dust problem. After all, mine started making noise the same day I got it. Also, dust noise is usually low pitched (rattling, etc..) not high-pitched.
High-pitched noise from an electric motor (a fan) is usually caused by the frequency of the PWM that controls the speed of the fan. I think the people that designed it used a human-audible frequency, which would essentially turn the coils of the motor into a speaker. That's my only explaniation.
If the above sounds like the problem you're having, don't bother dusting the fan. Just return it like I did.