I have a wonderful squealing noise whenever I start my Trooper up. I've
deduced that the sound is due to a loose belt. Where is the tensioner
and how is it tightened?

 

If it is a 3.2 v-6 then the tension is not adjustable as it's self adjusting, but the pulley that is on it might be going out. The unit is located behind the stationary fan to the left. If this is the case you might want to change the belt, pulley's and water pump as it is a pain to change.