engine noise

Just got back from holiday and started my 2003 S up after being standing for 10 days, and the engine made a clunking, metal on metal clackering sound for about a second, then it was fine. When it is running it is fine, does not make any noises , even deliberately labouring it in a high gear up hill and trying to accelerate. I have not noticed this before because it has not been left without starting for more than a couple of days since I have had it. Have just recently done an oil change using Fuchs Titan Super Syn 5w 40 full synthetic. Any thoughts or is it something I would expect . thanks