I got 02 Dodge Neon a couple days ago. The guy smogged it and everything before he sold it to us. Then my dad noticed that it shaked when we turned it on while it was parked. Also it shakes when ever we're at stoplights or we have the brake on. It doesn't shake to bad but it kind of vibrates. My dad thought it was the motor mounts so he replaced them but that didn't seem to fix the problem. What could it be and how much would it cost to repair?