2008 Holden Barina making tapping noise

Hi,

My 2008 Holden Barina has started making this tapping noise. The problem is intermittent, and whenever I take it into my mechanic (after driving about 45 min), the problem disapears. I think it might be the cold weather?

The noise seems to come from deep within the engine. The car only has 37,000 km on it, so I don't know why its having this problem.

I have uploaded a recording of the sound here http://1drv.ms/1HQY5oL.

Since I bought this car from a caryard, it comes with 3 months warranty. The guy said if they can't fix the problem, I can swap it for another car. They just need to find what the problem is first.

Thanks