If the motor on the sun roof makes noise it is just the spring. $5 to fix.AC depends on where the leak is. Probly under the dash like most of them. $8 bottle of R134 every other month.Knock in motor? Could be alot of things. I would reset the valve lash first. That might be the noise you are talking about. Fixing it is free if you have the right tools.But I still wouldn't pay much for it.