Why did people hear a lound rumble before the shaking began in christchurch earthquake?

Answer 1

Because Maoris are chacing a 10c coin

Answer 2

The loud rumble heard before shaking during the Christchurch earthquake was likely caused by the seismic waves created as the Earth's crust shifted. The waves can generate low-frequency sounds that travel faster than the shaking itself, reaching people before the actual ground movement begins.