If it's mains hum, then it's not going to be coming from the hub, as that only gets 12V DC, and the likely cause is a loose winding in the transformer in the PSU "brick". You can check if that's the source by covering the brick firmly with a cushion, see if that reduces the noise. That's for testing purposes, DO NOT LEAVE ANYTHING OVER THE PSU IT WILL OVERHEAT AND BE A FIRE RISK.
If it is clearly the PSU brick, then you can try phoning it in, or if you can confirm that it is the source then forum staff can get a new one posted out.
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