"earth" is connected to exposed touch-able parts on this coffee grinder. It does bite! It has the double insulated mark which per my standards is incorrect. It has an unearthed input. Schematic: http://imgur.com/QYaudyJ
The tingle you feel is the current passing from the one interference supression capacitor connected to the live leg of the mains input. The metal parts are effectively held at half the line voltage through a very high impedance (small cap at 50/60 Hz).
It is unlikely to hurt you unless the caps were to fail. The double insulated symbol is probably optimistic. I believe there need to be two insulating barriers between live and any exposed metal parts before this symbol is appropriate, in this case you have one cap that needs to fail before you get full line voltage, a bit unsettling but not all that rare.
If you are up to the task you could replace the capacitors with two modern 500V units if you suspect they are faulty, the tingling may be reduced but unlikely to be eliminated.
I forgot to add that if you have an earthed plug (and as Andy mentioned 3 conductor power cable) and it is in an earthed outlet you should not be able to feel any tingle and any such tingling should trip the residual current circuit interrupter if it exceed about 10 to 30 mA.
Sadly in Europe you can plug an earthed Schuko plug into an old unearthed socket so the earth protection situation is a bit primitive.