Have your dentist replace your silver amalgam fillings with a composite material. Your metalic taste is most likely being caused by the slight electrical current discharging in your mouth via your fillings. Read up on it here: http://www.drpgilbert.com/metallic-taste...
I don't think it's normal to experience tasting flavors from simply touching an object.
That said, if you are touching an aluminum case and you lick your fingers afterwards, it's possible that you could be licking up some aluminum dust.
Either way, I wouldn't recommend licking your fingers or your laptop.
I would try adding a colloidal minerals supplement in the liquid form to your diet to see if this resolves any mineral deficiencies you may have. Many of the minerals are metals. In chemistry the Theory of Equallibrium tells us that all touching matter exchanges atoms. I would also try washing your hands prior to touching the track pad. Colloidal/Ioniz
Look to see if touching other items brings this sensation. That may help you narrow down the cause of it.