I blame what have done Germany 80 years ago in Europe as the main reason, we are barely getting out of the phase were all people that lives through these times are dead but it is still rembered.
This is exactly what it is. That reputation has nothing whatsoever to do with the actual sound of German. The stereotype, btw is not about it being screamy, but ugly. People claim it sounds ugly and aggressive, for no reason other than Nazis. It’s a cultural stereotype that was completely projected onto the language, most notably how it sounds.
It could just be that for a lot of people their only exposure to German is that clip from Der Untergang where Hitler gets super pissed and it does indeed sound like yelling in German is way more aggressive than yelling in English - but the other people in the room don’t yell back at him and there’s nothing aggressive about their speech.
That and the videos of people pronouncing words in different languages and of course ambulance is said in a normal tone while Krankenwagen is yelled because stereotyp funni, but that’s based more on how the words look when written down I think.
