Have you ever been relaxing at night and then hear a faint, very high pitched electronic hum? I remember the first time this happened to me, it was a $5 USB phone charger I'd bought from a petrol station. Well, lesson learnt I thought to myself as I chucked it.
Unfortunately this TP-Link HS110 emits the same sort of extremely irritating high pitched electrical whine. I noticed it immediately after plugging it in and isolated the problem to the lights, as the sound changed in harmony with the flashing of the setup lights. Perturbed, I continued the setup (easy enough, TP-Link's apps are excellent) and hoped that once the lights were solid green the noise would go away. No such luck.
In summary, if this plug is going to be anywhere near your ears and you have decent hearing, it's not worth owning. A real shame because it seemed like such a bargain compared to the other offerings on the market at time of writing.