What are the symptoms of the fan belt tensioner going? Have a clicking sound, also an intermittent squeak coming from the fan belt area.

Is the tensioner meant to move up and down as the belt goes round?

 

Pull the belt of and check each pulley for play.

 

X2 on that, plus you can use a broom handle and press against each item (not the part that moves, but the brackets, mounting bolt, etc.) and press your ear to the other end, you'll hear noises very easily, and keeps engine noise from drowning it out. They also sell mechanic stethoscopes at the parts store.