Harleyjohn54

I think you might have this one wrong. My Sierra is at the dealer right now and one of the techs told me that there is a pressure valve that somehow runs the vapors from the fuel tank and unused fule through the engine. That's why you notice the "ticking" when you start your truck and depending on things like temp, how long the truck has been sitting.....ect determines how long this runs. I notice that it disapears when I've been driving on the highway for a while. I'll let you know tomorrow because they kept the truck and they are going to check it on a cold start.