I installed a couple of GU10 wall-mounted lights above my bed recently and it all went fine.
Tonight, I noticed a perceptible noise coming from one of them while it was off. Call it a hum or buzz, hard to describe, something you might expect from a low-quality transformer, for instance.
I switched the light on and off and the noise disappeared. I couldn't reproduce it. I tried to set the switch in middle position where the light would flicker and even then, no noise.
What would be the reason for this noise?
I don't think the light bulb can be responsible since the switch was open. Could it be a loose wire connection? It is easy enough to open and check the connection, but how could a loose connection explain that noise?
Notice the switch is part of the lamp. Any connection issue around the switch itself would probably be the maker's fault. I only had to plug wires into a connector ("recent" one, no screwdriver needed, like WAGO terminals, I don't know how these are called).
Obviously, once the reason for that noise is identified, I'm interested to know whether or not it is dangerous.
Edit: It occurred again this morning with no apparent trigger action. Switch open / light off.
This time I could set my ear right against the black box to confirm the noise comes from inside it.
It is definitely an electric noise, with a stable frequency.
I moved the arm of the lamp and it stopped and then again I couldn't reproduce.
I'll double-check the connections.
Still, I find it strange. If there was a shortcut, I assume the breaker would open the circuit.
Edit: I opened the box and noticed that a cable on a connection of the switch was a bit worn off, which could be an explanation. I "fixed" this with a bit of duct tape. When I put the current back, I noticed the noise again... but from the other lamp. Acting on the switch didn't silence it but it stopped when I moved the arm of the lamp. I checked the box and there is no worn off cable in this one. I also checked with a multimetre that all connections are fine and there is no short-circuit.
Also I noticed that phase and neutral were switched. In fact consistently switched on all the wiring I did that day (lamps, sockets,...). I just fixed this, wired everything right.
I'll see if the noise occurs again.
I did a bit a research to learn why switching phase and neutral is bad and I don't understand why it would result in that noise. The phase was not cut by the switch so it could reach the light bulb but that shouldn't be an issue unless another part of the circuit has an issue, right ?
(FWIW, I didn't mention this in the question as I assumed it wasn't relevant. The lamps are not mounted in the wall but in a headboard and the wiring inside the headboard converges to a plug that I plug in a wall socket. It was easier this way and there will be no work when I remove the headboard. From a practical perspective it means it is easy to check the connection from the plug to the lamps. It also means I got everything in the headboard (power sockets, USB power sockets, and lamps) plugged to a wall socket. I suppose ideally lamps should be wired to a separate fuse but I assumed it wasn't worse than former situation where all devices, phone chargers, lamp,... were plugged in a power strip.)