I understand the yz's tend to have a little more engine noise than some of the other bikes, however how much would cause an alarm to go off? I have an 07 450 and there seems to be a loud noise in the engine. It is not a grinding noise but more of a banging noise, kind of like hitting a metal pipe on a bench. I run full synthetic oil and change very frequently, plenty of coolant, and at times a small amount of a milky substance out of the breather tube. The engine seems to still have plenty of power and starts very easy. Any ideas on where I should start my search?