I have a 2007 chevy silverado that when its cold outside the low oil pressure light comes on for a second then the gauge will rise. When it is at idle the needle sits at about 29psi and driving is around 40psi. It also has started with a noise that sounds like lifter tap but its kinda random. I took it in to a shop and they checked my oil pressure gauge and it was correct and they also took a camera into my valve cover and it showed no oil getting to the top end of my motor. They said a couple of things it could be but i have no idea where to start im in need of suggestions!

 

No oil to top end at start up or all the time?

 

Well they said upon start up there was none and when it was revved up there was alittle but not like it was suppose to be.