Blades on hardwood floor have always been very noisy with the original beater bar. Maybe you stopped noticing it on the old blades as they started getting softer and more worn. You could slice a little off (as per viewtopic.php?f=20&t=15923
) or use a new brush bar which is renowned for making the neato quieter.
Just noticed there's someone selling a used one cheap on the sale board viewtopic.php?f=11&t=16615
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