I am having trouble with my Tahoe it has 200,000 miles. The knocking noise as heard on the video began very subtle and then became louder. Today the oil pressure dropped to zero. I plan on taking it to the dealership but I want to have some knowledge before I go.

 

I don't think I would start that motor again, especially with no oil pressure - sorry

 

The funny thing is when its parked it has oil pressure only when it's driven the oil pressure drops.

 

There's an oil manifold filter which get's clogged forcing a drop in pressure. It's a $6 part from the dealer. It's located under the oil sensor and in my case (2007 Tahoe 5.3) you need a snake arm to access. My mechanic has one of those and was able to replace the filter. Pressure back to normal.