Is it true that kohler has a service bulletin about engine chater on 2000 and older? I have a 23hp and at first I thought it was lifter noise when its first cranked up for about 30sec or so. Called my mechanic and he said something about the older kohler not haveing a way for the air to escape the lifter and that's the noise I'm hearing? It has about 800hrs and runs strong, doesn't use oil. Some days Ill mow and never here it and some days I think I here it when cutting but I maybe paranoid! I was told the new Kohlers have this problem fixed?