Discolored doorbell and humming transformer.

[Coyan]

My arlo Essential wired doorbell has turned an orange color and is causing the doorbell transformer to hum.

[DannyBearAgain]

I would suggest you safely remove mains power to the transformer before it catches fire.

 I would then suggest you to get an electrician to investigate before touching the equipment.

At a guess the doorbell has shorted out and loading down the transformer.

[Coyan]

I have 2 arlo doorbells. I disconnected the discolored one and that stopped the humming, so I'm assuming this is a defect in the arlo doorbell. 

[StephenB]

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@Coyan wrote:

 I disconnected the discolored one and that stopped the humming, so I'm assuming this is a defect in the arlo doorbell. 

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I agree with @DannyBearAgain that it might have shorted out.  If this is an AVD1001, then the power kit might also have gotten disconnected (or failed).

When was the doorbell purchased?  (Just wondering if it is still under warranty).