Ticking

Ticking was a noise which was created by a clock.

History
The Mysterious Ticking Noise was an instalment in The Potter Puppet Pals which featured a pipe bomb, creating the eponymous "ticking noise". (TV: Chute! Episode 9)

While reflecting on her 24 hours left to find the Doctor, Doom stated that "the [ clock was] ticking". (WC: Meet Doom - the Universe's Greatest Assassin!)