2007 Vauxhall Vectra

Noises problem
2007 Vauxhall Vectra Front Wheel Drive Manual 26300 miles

I have a 1.8 Vectra, which I've had from new, and for about the past 7 months, its been making a ticking noise when I start the engine, and lasts for about 5 seconds, it doesn't make the noise while driving. I took it to Picador Vauxhall, for an annual service back in April, and mentioned it to them, and they are baffled as to what is causing this noise, and left it at that, nothing else they can do. It has to be something, it never made this noise when I brought the car, and I'm worried that the Vauxhall Garage, know that come April, my warrenty will expire, and this noise will become worse, and then I have to foot the bill. On one occasion, I went to start the engine and it just failed, and it took 3 times to start it, which its never done before and never done since.
I hope you shed some light on this noise.
Thanks