Whenever I cold-start my bike, there is a loud pop pop pop noise that I'm assuming is coming from my exhaust manifold pipe...... I've tightened it down to make sure it isn't leaking and I see no holes in it. My question is, what's causing the pop pop pop sound when starting the motor up? It's never done this before, perhaps I need to take off the exhaust cap at the end and clean the pipe? Is the pipe clogged and just needs to be cleaned internally?