With these volatile times we are living in, where we are seeing racist views popping up more and more, it all got me thinking if the German people noticed a racist movement in the under-current of their population before the Nazi party was legitimized. And did they try to do anything to stop the spread of it?
I don't understand the question. The NSDAP was openly antisemitic and thus racist. It was founded 1920.
Also antisemitism was widespread not only in Germany but actually in all of Europe (and e.g. the USA), for centuries. First on religious grounds (jews crucified Jesus, you know), and at least since the book 'An Essay on the Inequality of the Human Races' by a certain Arthur de Gobineau even on 'scientific' grounds.
Since Prussia had occupied large parts of Poland during the 3 Partitions of Poland 1772 - 1795 Germany, that had been unified by Prussia until 1871, had a significant number of lower class poles in it's borders, on which had been looked down even more than onto german low classes. That had racist undercurrents too.
You should read a Hitler biography, good ones detail the social situation as well. There are e.g.:
Fest, Joachim - Hitler (exists in english translation on Amazon)
Kershaw, Ian - Hitler
Also interesting, since it shows the social situation in Vienna before WW1 (that's in Austria of course, but it shows in some parts how racist european societies were already before WW1):
Hamann, Brigitte - Hitler's Vienna
For the situation in Berlin and Germany in general between the wars, from a conteporary POV:
Roth, Joseph - What I saw: Berlin 1920 - 1933
Tucholsky, Kurt - Deutschland, Deutschland, Uber Alles: A Picture Book (but has lots of texts by Tucholsky, RH)
Contemporary novels:
Fallada, Hans - Little Man, What Now?
Roth, Joseph - Das Spinnennetz (there seems to be no translation, an english version would be called 'The Spider Net', I guess)
Also interesting:
Haffner, Sebastian - Germany: Jekyll And Hyde: A Contemporary Account of Nazi Germany (written 1940 in England)
Haffner, Sebastian - Geschichte eines Deutschen: Die Erinnerungen 1914 - 1933 (for some reason I can't find an *english* translation of this book, the french one is called 'Histoir d'un Allemand. Souvenirs 1914 - 1933, so I guess in english the titel would be something like 'History of a German: Memories 1914 - 1933')
Regarding people trying to stop the Nazis:
Sure, writers wrote books, Songs and reports, all sorts of people were holding speeches - and especially in the 1930's there were lots of bloody clashes between the Nazis and Communists and Social Democrats with lots of people wounded and even killed. Read the books.