why did they give me new license plates when i got my regestration it was expired scince 09 does that have any thing to do with it and will my insurance still show up when they scan my plates?
It's likely you have something loose in the suspension, like a stabilizer link, or maybe a worn ball joint. It needs to be inspected by a competent mechanic.
4' on center will be more than enough, and will line up with the wall studs. You'll only need 3 if you start 18 in from the ends , or 4 if you start 6 in from the ends. 4 might look better and stronger if you dont hit studs and need to use plastic anchors.
