Any other gears inside the cassette box, really aren't necessary. So feel free to remove them if the cassette is making too much noise (shown in 2nd photo).

Edit 3/14/2019: All cars are different. Many people in the comments have had luck keeping the center gears in the cassette and removing the interface gears. And also vice versa. Play around with it! If you can get it to work, awesome! If not, then try something else. Don't give up until you have your music playing in your car! Cheers!