It's always hard to distinguish accents in languages other than your own, but...
...I'd encountered bits of Schwyzerdütsch in my college years: several classmates had grown up in Switzerland, and sometimes the dialects of different regions of the German speaking world were discussed in class. But the classmates that spoke Swiss German were all either Americans that had learned German Standard German first, or Swiss that had emigrated to the US at a young enough age to speak English with no detectable accent, and then taken German as a "foreign" language in high school / college, so they spoke Standard German with about the same accent taught in class.
And then on Youtube today, I came across a video with a Swiss guy speaking Swiss Standard German, and... wow. It's not that the accent was impenetrable: I could understand every word, but it was so different that my conscious mind took a few seconds to realize that my Wernicke's area was successfully parsing it. One part of my brain was delivering meaning before another part flipped the "I know this language" bit on, and there was something in there that kept trying to flip that bit back off. Your brain is like a B-36: a collection of parts flying in loose formation, and when the illusion that it isn't is broken, the experience is quite surreal.
It's kind of a different twist on an experience I had in high school: We were watching a movie in German class, and a character, out of the blue, started speaking in English. My mind took absolutely no notice for about the first sentence: I'd understood what was being said in German, I still understood what was being said, nothing to see here. Then my brain did a huge double-take.