2.5 L Subaru engine. 10500 miles on it. Change the oil three times in it's short life, don't abuse it, but, do run 85 mph for some trips through Florida (wow, some people really drive fast down there). Have Castrol 0-30 synthetic in it since 8500 miles. Suddenly, the past two days, I have a lifter that is very loud for the first 2-3 minutes after cold start-up. VERY different than this engine has ever done before. Car has been performing great, 30-32 mpg at highway speeds, 27-29 mpg in city. Only thing that is different is a magnet I put on the oil filter...that can't possibly be contributing this lifter tick. Just keep on driving it, or is this a problem that needs to be addressed?