It could be the result of the rust. I have actually had brake pads that were designed in a way that they would collect brake dust and make noise. You could take them apart and clean everything with brake cleaner. I'll often take sandpaper and clean the glaze off the pads and rotor as best as I can. The rotor is a bit more difficult to clean.
Also, they make a brake squeal eliminator you could get. It is placed on the backing plate of the pad which helps eliminate noise. See the pic below for an example.
Here is a link that explains in general how to replace the pads and rotors. I'm not suggesting they need to be replaced, but rather providing directions for taking them apart to service them.
https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors
Looking at the rotor, it does appear a little rough. Is the opposite side in the same condition?
Let me know.
Joe
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Wednesday, January 19th, 2022 AT 5:20 PM