NEVER mess with the safety ground. Its purpose is to carry all the fault current and blow a fuse,
or trip a breaker. Inserting any component in that path, diodes or other, is extremely dangerous.

Instead, you may float the AUDIO circuit from the chassis, or connect the audio circuit to the chassis
through an impedance (R, C, diodes), to address noise problems. But do not touch the safety ground.

An article about noise in audio amplifiers:
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf

Has this happened before? If it is new feature it could be caused by insulation damage on transformer -> electrocution danger -> throw out the charger and not repairable.

Other possibility is that you have so sensitive voltage detector that you saw normal very low current (safe level) capacitive leakage from mains to output.

We often hear reports of weird noises coming from the audio interfaces when attached to a laptop. Sounds a lot like electrical interference, mixed with scratchy data type noises and combined with mechanical noises triggered from hard disks or mouse movement. The sort of noise can vary but the cure is always the same — pull the power out of the laptop and the noise goes away. Laptop battery life is not all that great so running on batteries is not an ideal solution. So what’s causing this issue and how do we cure it?

To everyone who asks how to remove the noise in their particular and specially unique situation – GET A HUM ELIMINATOR!

Designers rarely analyze the cumulative effect of capacitor tolerance on the total leakage current; errors of capacitors are verified by testing. Modelling helps reduce production costs and improve quality while ensuring leakage current requirements are met in medical applications.