I've read other reviewers comments about exactly that, a high pitched whine like a camera flash charging up. All I can say is the one I got is perfectly silent. I keep it on my nightstand and have never heard anything.
My brief testing on this seems to indicate that the 5 ports on the 40W USB charger (which incidentally is now available in white, too) are all the same -- you can plug any device into any port. I have tested only with non-Apple devices, though.
We bought this charger and plugged in our PS3 controllers and they will not charge. It works for our tablets (Apple iPad mini and Air, and Nook), the Wii pro controllers, and the PS4 controllers.
It doesn't work with the PS Vita, the PS move controllers, nor PS3 controllers-- basically if it's associated with PS3 it doesn't seem to work.
Nope, 5 volts output at all times. Devices are usually designed to swap to a trickle charge once the battery reaches a certain level. Also with lithium and metal oxide batteries memory affect is not that big of a concern.
Most complaints were due to the ports failing. The old units had a hardware fuse on each port. If it blew that port would no longer work. The new units they are replacing them with have breakers on each port which reset after everything has been unplugged and the unit sits for 20 minutes or so. I have 2 of the new ones and the breakers to my knowledge have never tripped.