I've got a question...when I grab the top of my drivers side rear wheel & tire and pull and push (like I'm trying to "rock" the truck) it knocks a bit...not real bad, but kind of like if the lugs were not tight and the wheel was loose. I know they are tight, I even check it. Would this be a bearing or something thats worn? The passenger side does not do this, nor does the front...just the drivers side rear...Thoughts???? I should note that when I put the E-brake on, the knocking goes away and it feels solid and not loose like above...don't know if that helps????