If it went away after the oil change it's most likely a sticky hydraulic valve lifter.
There oil additives available from Halfords etc. which claim to help.
Another common fault on these is a leaky exhaust manifold, which causes a ticking sound which generally fades as the engine warms up.
This is usually caused by a small crack in the manifold or failure/loosening of the manifold bolts at the alternator end of the engine. You will have to remove the heat shield to get a proper look.
gibby
July 2009