2005 mercury montego brake lights

your hearing the clicking noise because your computer board in the tail light unit is shorting out you will always here a clicking noise by the shifter because that noise is the relay from the brake circuit telling the shifter to release because your foot iis now on the brake and we can shift into gear. Now one other problem is the switch in the brake rod itself just above your foot, that switch comes loose aand makes the brake lights flicker.... With mine i layed on the driver side floor upside down removed the unit and clued a piece of rubber to it and bolted it back on now the switch works fine. If your cruise works and then sometimes does not its that switch.