engine knock at start up

After the dealer changed both of my faulty exhaust manifolds a few weeks ago, I opened the hood because I was going to change the oil. I found that my oil dipstick was MISSING! I called the dealer enraged as to how this could have happened. They agreed to give me a new one and change the oil for free. I took them up on it, but ever since, the truck knocks on start up. I'm ready to drive it off of a cliff.

No, I think they are morons. I'm guessing that the different brand oil and filter have something to do with it. They offered to "look" at it which usually means "we couldn't duplicate the problem" or "that's normal."

I'm at the point now that I don't trust the dealer to work on my truck. This is only one of a long list of incidents that have occurred at this and another Nissan dealer. I really like the truck, but I will think more than twice about buying another Nissan, mostly because the dealers I've dealt with have ruined it.

I noticed another thing on my way home from work today--After I started it and heard the knocking again, I pulled out and watched as my oil pressure went right up to the high mark. It stayed up there and slowly came down as I got to speed. It stayed on the high side until the truck warmed up. It never acted that way before this knocking issue. Again, I have always ran Valvoline 5w-30 with Fram HD filters. The dealer says they use Nissan 5w-30 and Nissan filters. Who knows what the quality is. I'm thinking of changing it out to my usual to see if it makes a difference.