2000 Jimmy Lifters are tapping while engine cold till it warms up after several mins than the tapping goes away.Is this the sign of a major issue or does it sound like the lifters are just sticking? I am also losing coolant but no signs of a leak and no apparent head gasket leak symptooms either.I had the coolant system flushed out because it was terribly gubked up.This vehicle has 196,000 miles on it but other than these issues is in excellent condition.Suggestions???