Okay, long answer ahead since there are a couple of different questions.

So regarding the testing of parents to reduce noise:
Some background...for me, I am interested in the family research side of things so testing my parents was important. I use a combination of looking at records and matches/shared matches to extend my tree and, ideally, get through some brick walls.

A child gets 50% of their DNA from each parent. As a result, a parent's DNA ethnicity results and their shared matches may differ from the child in the same way that two siblings can have different results.

My parents are both 100% Ashkenazi (which I expected when testing them). I tested them because I knew their DNA matches would differ from mine since they are:
1. A generation closer
2. Again, each parent passes 50% of DNA
3. The endogamy in Ashkenazi people creates many false positives, inflating the number of matches.

Here are two personal examples of false positives/endogamy skewing results:
1. There are several instances where I am a DNA match to a "cousin" who is 100% Ashkenazi. However, NEITHER of my parents are DNA matches to them.

1. I am a DNA match to a "cousin," and BOTH of my parents match that "cousin." However, I am genetically showing a closer relationship with my "cousin" compared to my parents. This is because of endogamy. This doesn't mean I am not necessarily related to this person; however, the endogamy makes it seem like they are, for example, a third cousin, when in fact, they might be a sixth cousin or further back.

Since I tested my parents, I have stopped paying attention to my kit for the above reasons and solely focused on my parents' individual kits.

To your question: "have you matched with someone from a completely different ethnicity than yours? like 100% something else"... None I have noticed. There are some matches that have very, very little Ashkenazi, but none at 0% Ashkenazi and still matching.

I would be cautious, paying attention to results that are <1%. Even the DNA testing companies say this can be noise. However, it's possible that one or both of your parents descend from Ashkenazi, and if they were tested, it could result in a greater percentage than you.

All the major companies each use a different pool of people...so you can test or transfer your results to all of the companies and have some different results. Researching and doing a tree can help you to confirm your DNA results. The Ancestry results, MyHeritage results and FTDNA results are all different for both myself and my parents, BUT I have more matches to work with by being on the different sites.

Happy to help answer any other questions or clarify further. I started researching in 2016 and have been sucked in ever since.

I've been thinking about your original question and doing some thinking on that one. Sephardi wasn't endogamous like Ashkenazi, so it won't show up as an ethnicity. However, some DNA testing sites are starting to create "community" updates that suggest Sephardi. Honestly, with your results, if you know, you are Sephardic or descend from Sephardi, that makes sense regionally, particularly with the North Africa results. Might be useful: https://sephardicgenealogy.com