2000 Ford Explorer Limited Leans to Driver's Side

Hi. We have the above vehicle and a short while ago we noticed that it had a slight lean to the driver’s side, an equal amount at both the front and back (by eyeball). It does not seem to affect the ride or driving. It does not seem to pull to the left. We took it to our regular mechanic and they could not identify what the problem is. We explored the web and could not find any reference to this problem reported by anyone else. Any ideas on what we should ask the mechanic to check out?