Slight knock after dealer oil change

So my truck has had every oil change done at the dealer every 5k. I bought it with 120k on it, and it runs great. First oil change I did myself and used part synthetic blend, and it continued to run fine. Took to dealer (different dealer then its previous owner) for next oil change, and I can almost swear there is a slick knock now. It's not all the time, but I definitely hear it.

First heard it slowly going up a hill (low rpm). It lasted for about 5 seconds until I got to the top of the hill. I turned around to see if I could repeat the issue, and it did it again. I haven't heard the knock as loud since, but it seems to be louder then before oil change.

I've narrowed it down to a few possibilities, and wondering if you guys could lend some advice.

1. Just "spark knock" that is common with the 4.0 and run better gas.
2. Different oil weight or cheaper oil then used before.
3. It's always done it, I just didn't have my radio on this time.
4. I'm crazy and need to not worry about it.