My 96 2.0L petrol has 90K miles. Recently at start up I hear a low screeching, which I believe is a valve sticking. I had the same sound coming from a Primera previously and sticking valves was the problem. As an oil and filter change is due should I add Slick 50 or similar when I change the oil, should an additive fix my problem? The noise only happens at cold start and lasts for about a minute of driving, also it stops with increased revs. Will it get worse if it is not resolved? Regards Eddie.