Hi All, My name is Brian Bittner and I live in Pennsylvania. Proud owner of an 06 Silverado Quad Cab. Love the truck! Within the last two months, I started getting this tapping noise that would come and go as I would drive. I did some snooping around and the item that is making the noise is located under the plastic VORTEC housing. It sits vertical with a blue cap on top with several wires coming off of it. Any thoughts what the heck it is?? I tried looking for a diagram of a Silverado motor and I did not have much luck. Truck runs great, this tapping gets a little annoying at red lights and stop signs. Thanks and Merry Christmas to all!!