Trying to track down intermitten squeak

Like the title says, I've recently developed an inconsistent squeak while driving, it comes and goes and is usually very brief, but always while moving. It sounds like it may be the drivers side rear, but not entirely sure about that. I know my drum shoes havent' been changed since I bought it 4 years ago, last time it was inspected they checked out ok and I've never had braking issues so I've left them go, could worn shoes cause squeaking without braking? Other causes to look into?

Don't know if it's related or not, but a couple days ago I developed a fairly severe vibration while driving home. I tightened the rear ubolts and it seems to have gone away.