Ford F-150 (2009-2014) :: Can Synthetic Oil Cause Engine To Make More Noise?

I recently posted a thread about my 2011 5.0L F-150 making a knocking sound that I was unsure about. Here's a link to that thread. [URL] ....

But my question here is about oil. My truck is still making that damned noise, it seems more audible sometimes and less so others. But it ONLY happens when the engine gets warmer. The noise is completely absent when I do a cold start in the mornings. I've been trying to figure out if it always made that noise or not...I do remember a few years ago when the truck was brand new, pulling up at a drive through window for coffee and noticing that there seemed to be an excessive amount of engine noise echoing off the brick building. But other than that it never sounded out of place to me.

I only started noticing this knock after my most recent oil change, which for the first time ever in this truck, I went from using the Standard issue Motocraft 50/50 synthetic blend oil to using Mobile full synthetic.

Now, I could be totally off base with this...But is it possible that my trucks engine is making more noise due to the thinner synthetic oil? I am considering going back to the MC 50/50 blend oil to see if it makes a difference. Also it's worth noting that this knock really only seems to be present below 1000RPMS. When I'm actually driving and pulling between 1500 and 3000 RPMS the engine itself sounds and feels as smooth as butter. On that note, it idles perfectly smooth as well...It's just the noise below 1K RPMS.