Internet Router has a high pitch sound?

quite a number of routers either have this fault straight out the box or develop it after some time. I have seen it in all major brands of warying types and function.

It varies in intensity from barely audible to quite loud in some cases, and is usually ranges from between 8-20khz. It may vary in tone and volume with load or traffic, or it may be constant. Most people believe it is the power supply unit (adaptor) or induction coil that has come lose, but this is actually inaccurate. Most of the time this is a semiconductor problem that cannot be cured.

Your main options are 1.) if it is a new device, return it and get it replaced. 2.) If it is an older device out of warranty you could relocate it to another room, or cupboard under the stairs (or similar) where it won't be such an issue. 3.) you could replace the unit. (expensive yes) but quite often these high pitched noises cause irritation, distress and headaches sometimes without the user even realising the router is the cause. 4.) you could enclose it in a ventilated sound dampened enclosure, though I reiterate it must be ventilated uless you're happy of running the risk of setting your home on fire. 5.) smash it with a sledgehammer for satisfaction, especially if (as in option 3) you have been distressed by the noise.

Most of the components that cause the issue are surface mounted and not easily replacable. I have seen too many people guessing/speculating about the cause of this problem but RARELY is it a power supply or induction coil or any other component that a standard electronic serice engineer would be prepared to fix.