We first noticed the vibrations the first time we bought an electric blanket. If one of us is under the blanket with power on, and the other runs fingertips over the bare skin of the one being nuked, there was this gentle rrrr sensation. Power off, no thrill. Full details are to be found in the latest Tralfamadorian manual of cognothrillistic transinformatics, available in plain brown-paper envelopes at your local branch of Vonnegutian hypersemination for the list standard counterquantitative determination of emolumoleons per page. Book immediately to beat the Xmas rush and the sharks' mark-ups. For lower detail at lower cost, I wave my hands and talk vaguely about induction and all that. That is why you only feel the effect in point contact (press firmly and the sensation vanishes) with a conducting surface such as skin or metal. Essentially you are feeling 50 cycle hum directly. (60 Hz if you happen to be in the US, right?) For best effects gentle stroking with dry skin seems to work nicely. This no doubt causes current flow that is only intermittently enough to stimulate the nerves in your fingertips. My guess. Your move... Cheers, Jon

I've felt this myself on my Hi-Fi aplifier. I always thought it was slight vibrations from the transformer in it. AC induction in your finger nerves!? 

I have noticed this effect in both small domestic appliances and also in large industrial equipment. I both cases it seems to be an interaction between a magnetic field from electrical transformers and the metal case of the equipment. The alternating magnetic field of the transformer seems to induce a small voltage into the metal. These metal parts should be earthed, but hey, no-one's perfect.

I don't know what the electrical process is that causes this effect (there may be more than one) but I often feel it when touching domestic electrical equipment connected to mains supplies (50Hz and 60Hz both, as I'm British but work in Saudi Arabia).

SlimJim is right in his comment about earthing (grounding), as it seems to occur mostly in ungrounded equipment that operates on 2-pin plugs. The casing metal - it doesn't make much difference if it's bare or painted - apparently acquires a "floating" voltage that gives what I feel as a mixture of vibration and tingle.

There is, however, a solution: if you feel the tingle, turn the 2-pin plug upside down and it will disappear or at least become very much less noticeable. For anyone in UK or France: Sorry! You can't do this with your grounded plugs, but it should work in Germany.

The vibration is due to the working of electronic components in the laptop, especially the processor.