being shocked by Amp casing

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

is this dangerous?

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?