The 5.3 Liter in my '01 Chevy has had a knocking noise at startup since I bought it new. That noise continued to get worse, and despite a letter from GM stating that this noise was normal, I looked for a solution. What I found was a Bosch filter with a check valve which helps keep the oil in the engine after it is turned off. If I run that engine today, there is virtually no knock tomorrow when I start it up. However, if I run that engine today and let it sit for a day or more, that knock returns as the check valve does eventually let that oil slip past it and back into the pan. With 235K on this original engine, this filter helps keep it going; and with the price of new vehicles, that's a big plus. I understand that AC akes a filter with a check as well, although I have not tried it.