Noisy Omega - Mr. D
98 2.5 V6, runs great, tick over is fine but when I first start the engine there is a loud 'clacking' noise which could be a very, very noisy tappet! Speeds up with the engine as it is revved. The noise disappears after 5 minutes or so - when the engine is warmed up? Worst when the engine is first started in the morning but also happens if the engine has been stopped for a short while and restarted.
Noisy Omega - Dynamic Dave
Sounds like a leaky hydraulic valve lifter(s).

See this recent thread on a Vectra for some suggestions.

www.honestjohn.co.uk/forum/post/index.htm?t=40902