differential fluid

My 07 Element LX is the first car I ever bought and I would like it to be the last car as well, so I take care of it by doing whatever the Maintenance Minder tells me to do and whatever the Honda Service Center recommends. Well, I've been going to my local service center in Woodside, Queens, NY...

After searching posts, I was convinced I needed to have my differential fluid changed..... After going to a "honda" shop, they told me I don't have differential fluid in my car. So, obviously they couldnt change it for me to solve my noise/knocking problem on turns and uneven inclines...