A switching mode power supply is very efficient in its working. Although, the supply is designed in such a way that it produces noise that is inaudible to the human ear, it sometimes gives a lot of noise especially when it gets old.
The good news is that if your switching mode power supply is producing a lot of noise there are ways in which you can eliminate the noise.
High-pitched whine without a fan
This noise is usually caused by external electromagnetic interference (EMI). To solve it you need to move the power supply away from anything that produces a large amount of EMI. Some of the objects that tend to produce a lot of EMI include: large speakers, large batteries, fluorescent lights and flat-screen monitors.
If you remove the supply from these objects and the noise persists, it must have been caused by a dry capacitor. You should remove the capacitors together with the soldering iron and then replace them with new capacitors.
You should note that capacitors have the ability of causing massive electronic shock; therefore, after unplugging the power supply you should leave it unplugged for at least three hours before you remove the capacitors.
High-pitched whine with a fan
The noise is caused by lack of lubrication in the fan bearing. To eliminate the noise you should lubricate the bearing. This calls you to unplug the device from the power supply and remove the fan's bearing protective plating. You should then put a few drops of sewing machine oil directly onto the bearing.
You should note that some protective plating is held by screws while others are held by a thick sticker.
If the low-pitched hum is annoying, you should put the supply in a metal casing in order to shut the noise in the casing. All you should do is to visit your local store and find a casing that will fit your entire power supply unit. You should then place the supply inside the casing and screw the casing shut.
These are some of the ways in which you can eliminate the noise in a switch mode power supply unit. If you do all of the above and the noise persists, you should take your device to a professional who will rectify the problem for you.
To ensure that your device lasts for a long time without developing problems, it's good that you buy your device from a reputable seller.