When was the oil last changed?
What grade and type of oil did you use?
Did you use a proper oil filter from the Vauxhall dealer spares dept? Other filters may not have the non-return valve which leads to slow oil pressure build up.
If these things are OK it could be a failing cam chain tensioner, which should be replaced ASAP.
If it was mine I'd replace the complete chain kit to be on the safe side, if it fails will cost a lot more to repaiar the damage than it will to fit a chain.
jimbo, March 2011
