Without hearing the high-pitched noise it is mostly likely related to the speed, or number of revolutions, the centrifuge is operating at and a small imbalance which at high RPM is causing a vibration which results in the noise.

Not knowing too much about centrifuges it could be as simple as a loading balance issue as above or bearings, motor windings or driveline wear.

Depending on the motor, electric induction motors do have a high-pitched tone when under high speed load.

Thanks so much. Since it was making the noise after cleaning the rotor and without any tubes in it I contacted our facilities team. They took it apart and found rust and and a cracked plate surrounding the rotor spindle. Probably time to replace it.

Glad you found the cause.