My Jeep Liberty starting making the same type of 'boom' noise it makes when you try to make a sharp turn in 4-wheel drive, but it's not in 4-wheel, & it happens even when driving straight. The noise/bump feeling is not loud, but I don't want to drive it. Any ideas before I take it to a mechanic?

Not sure what you mean by a "boom noise in 4-wheel." Nothing should be booming in 4-wheel or not. Have you had the front end parts and u-joints checked?