Your humming transformer is your quaterback
Got mechanical hum. Deploy the DC Blocker.
Many amplifiers have a really annoying mechanical transformer hum (emitted from the transformer itself), especially equipment with toroidal (circular) transformers.
You can hear it when you place your ear close or next to the chassis.
This is usually caused by a small amount of DC voltage in the mains which makes its way through to the mains transformer, it will become ‘saturated’ and start to hum like a trooper.
The DC Blocker is a clever device that you place at the IEC (at the rear power inlet) and as its name implies, it stops DC from getting into the audio mains. It eliminates transformer hum from amplifiers.
Behind every good component is a DC Blocker
Just deploy at each component. Remember that best practice is to always keep at least one direct power cable connection.