astra 1.8 auto making noise when hot

[yogimyster]

Just bought a Holden Astra 2003 sxi 1.8 Auto for my fiance,car has done 90,000K and just had a full service including timing belt been changed. Starting the car 1st thing in the morning it sounds great but when it's up to full running temperature it makes a noise like the valve clearances are wrong. Could this be the wrong oil in the car??

[AlBags]

If this is the GM car, then they have hydraulic tappets .. yes .. It's possible oil is incorrect. Clearance is taken up immediately after starting and oil pressure builds, and they should be very quiet. After a lot of miles, the odd one may tap a bit, especially when hot. This means changing the set, really. Not cheap.
If this started after an oil change, you should check to see what viscosity oil has been used. It should be a low value, like 10w30 or 5w ....
Also check if it requires synthetic, semi-synthetic, etc.