Are you absolutely and completely sure that it hasn't always heated up like this; or is it just that you've only just noticed?
Depending on the layout of the charge system, if the transformer (for 'converting' electrical outlet power into the smaller doses used by your laptop's battery) is built in to the laptop, then this heating is perfectly fine. The transformer has to do something with all that energy, and since it translates it through a magnetic field, that creates a lot of heat energy as a byproduct.
Mind you, if you're leaving it in while fully charged this is generally unadvisable. While in theory the laptop should automatically realise "Oh hey, I'm on AC now" sometimes they do get a tad confused and start using the battery and AC, leading to a constant charging, and much overheating.
All in all it's not something I would worry about too much, as long as you keep your eye on it.
On the fan-brightness front I won't comment, as that's nowhere near my field of limited expertise.
