Drove my truck home from work lastnight just fine. Needed to go to the store about two hours later. Started my truck up, but when I did at the end of cranking the engine made one extremely loud knock, like someone hit the hood with a hammer, so then I turned it off, and one more loud knock. Started it again, the exact same thing. Drove it, acted just fine no knocking or anything. When I started it this morning no knock, drove it to work, then when I turned it off another loud knock. Has anyone else had this problem.