With the truck at idle, I hear a light popping noise coming from the stock air filter housing. I would say approx 2 or 3 "pops" per second at a continuous rate. It is more pronounced with the hood open. The air filter restriction gauge and the filter itself look ok. It is not the oil pump tick as I have that too. Is this popping normal turbo diesel intake noise? I am used to a "hissing" sound at the intake of gas engines. This is the first diesel engine I have ever owned, heck the first turbo diesel I have owned. This truck is awesome! I can never go back to gas. Thanks.