Why do some Inline 4 sound more refined than others?

I was shopping for my next motorcycle, like we all do...And I came across a few mid tier inline 4 naked motorcycles that I like.Kawasaki z900 Honda Cb650r Suzuki gsx s750Now, when I heard the exhaust sound of the Kawasaki and Honda, they sound very refined and don’t have that idle rumble like the Suzuki. The Suzuki sounds louder for some reason too. And it’s just a slip on.Suzuki: https://youtu.be/JN1miCI_AmwKawasaki: https://youtu.be/KpZIZ2CwKa8What would the reason be for that?Thanks all :) via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/e6ympa/why_do_some_inline_4_sound_more_refined_than/?utm_source=ifttt