I've recently discovered fairly loud Fizzing/Buzzing noise coming from the consumer unit ONLY when the electric shower is on. The shower is about 16 years old, 7.5 or 8.5 kW power rating. Consumer box is in hallway, inside a cabinet, so couldn't hear noise with cabinet doors closed. No other noises or issues with electrics in house, no burning smell or marks around consumer unit, no melted bits. Is this noise normal?
A loose connection for that circuit is likely, which is a fire risk. Also, a faulty circuit breaker (fuse) sometimes generate noise. Either way, an electrician or competent person should be contracted without delay.
This noise is not normal, you could have anything from a loose connection to a faulty MCB. You need an electrician to investigate it as soon as possible.
In the meantime switch off the MCB for the shower and don't use it until it is checked.