Why does my wife's skin buzz when she's using her laptop? When my wife uses her laptop, if I touch her skin, I can feel a buzz.  She doesn't feel the buzz, but she can hear it if I touch her ear.
So I'm guessing it's a faulty laptop, and she's conducting an electrical current.
But why would she not feel anything, and what would it be that she would be hearing when I touch her ear?

More info:
The effect is only intermitent - it's pretty reliable in a single session on the laptop, but some sessions it won't happen and others it will.
I had the same sensation with a desk lamp that I had several years ago, with no moving parts (as far as I could tell)
The effect only occurs when I move my finger - if I'm stationary, I don't notice anything. 
I was playing with my son, and noticed the same buzz.  First I thought he was touching the laptop.  Then I realised he had skin-to-skin contact with my wife who was using the laptop.
 A: This effect occurs very often when touching electronic devices that are connected to the power mains.
You can verify that it is the connect to the power mains: unplug the power adapter and all other connections to other devices connected to the power mains and try again.  The effect will be gone away.
It can best be felt also by the person touched if you touch with one finger only and move the finger (you can feel the difference on conducting surface areas of the device also).
What you are feeling is inducted power mains frequency so its probably 100 Hz (if you have a 50 Hz power mains or 120 Hz if you have 60 Hz power mains).
You can see this inducted voltage if you hold single-endedly the tip of a oscilloscope.
A: Its due to residual transductance of the live AC current into the shielding of the device. Get an earthed plug and it will disappear. I've experienced the issue in dozens of shielded but unearthed electrical appliances, not just laptops. It feels exactly like a vibration (when you move the finger over the surface) but it's not, my guess is that the mechanoreceptive nerve-endings in the skin react to the small current. 
A: I felt this and even drew sparks from it on a product I was working on, and was very worried, but after a lot of research and the standard government safety testing, it was deemed normal.
A small amount of touch current is allowed because it is not considered harmful.  It happens with devices which have isolated transformers but the primary side is not grounded.  There is a small amount of capacitance across the transformer isolation (especially in switch-mode power supplies, which require extra capacitance here to prevent EMI), which means the chassis will be at line voltage relative to Earth if you measure it with a voltmeter, but the capacitance is small so no significant current can flow.
If you concentrate the current to a very small point (by brushing two metal surfaces together, so that microscopic spikes touch each other momentarily), the metal will melt and make sparks.  If you press the metal tightly together, nothing will happen.
If you ground yourself and then brush against the metal very lightly with a finger, especially on a corner or point, you will feel it, because it is high voltage and stimulating a few nerve cells at the tiny point of contact, but if you press hard you will not, because even though more nerve cells are in contact, your body's resistance/capacitance is grounding out the object and the voltage drops below the threshold of sensation.  I also noticed that if I rubbed a shielded object against my skin (the shield of a cable), the friction sensation felt different with the power on and power off.
A: 1 -  Use a voltage detector pen in USB connector GND to see if there is a bad isolation between AC ground and DC ground (this is first option not because probability, but because it could be dangerous). It's normal a little fugue current between primary and secondary of transformer but the AC plug have 3 conectors, 2 for voltage and the third  is for GND (ground), perhaps your home installation haven't a good grounding, check that! is very important.

2 - Beware of what is on your wife's laptop screen when her skin buzz =P
picture source
A: I agree with jonathon that it is vibration, although it is far more likely to be the laptop fan, rather than the hard drive
Why she doesn't feel it? The human body has vibration receptors, and I'm sure she notices the laptop vibrating when she turns it on. However, like with all constant stimuli, but particularly touch, our brains are great at blocking them out. I suspect that the fact it happens to her whole body makes the effect even greater, as there is no sensory discrimination from different nerves
You touch her, and two things are different. For you, it is a new sensation, and it is occurring in your hand alone. If you held her for a while, while focussing on something else, you would probably stop noticing
I would argue that this is a physical effect, biophysical to be precise.
