Useful information - but existing questions and answers have focused on explaining the why and have not gone into detail on what to look for when diagnosing and distinguishing the two. So, one type of noise can be safely ignored, the other is very serious and is a reason to stop using that particular charger.

There's a comment that a 'charger that generates coil noise especially when under load may be defective' (which I believe means, if the noise occurs when the laptop is connected, but not when the charger is connected to the mains without being connected to the laptop).

A 'crackle' or 'sparking' noise is potentially a sign of a failing transformer, and a potential fire hazard.

A 'hum' or 'whine' is relatively normal, and likely an innocent by-product of the transformer using electromagnetic plates to convert current.

and and have learnt that there are two very different phenomena - one serious, one harmless - which cause observably different noises to come from a charger: I've read existing questions and answers on noises coming from laptop chargers (e.g.

Laptop charger making noise