You are not going crazy.

http://www.youtube.com/watch?v=bd2B6SjMh_w

I had never noticed this ticking or buzzing in the AC4U until you pointed this out. Now I will be driven crazy by the knowledge that there are sound emanating from my N800 chargers. Argh.

I have examined various manufactures' switching type battery chargers. These AC4U Nokia chargers are fine devices compared to most others. I have attached some photos below for those of you who are curious about what is inside. As can be seen, there are quite a few components. In one photo I label the key parts. The audible ticking emanates from the high frequency powdered ferrite core transformer. This transformer is pulsed in bursts when the N800 battery is full. The bursts in mine were close to, but not exactly, one hertz. That is why you hear what you do. Enjoy.

M5