My Mazda Tribute 2003 is in good condition, with two previous owners and only 147,000 km. However, it suffers from a loss of power and a loud squealing noise when I accelerate...

What you might find is that the loss of power and the squealing noise could be completely unrelated. In any case, a loss of power can be caused by any number of problems, so an electronic scan of the car would be the first move in diagnosing that problem.

You might be on the right track, meanwhile, in thinking that the squealing noise has something to do with the rubber drive-belts in the engine bay. These will often emit a high-pitched squeal if they get moisture on them. Typically, this will be coolant from a leaking water pump or a leaking radiator (both of which are located handily near the belts). Even though the belts may be perfectly tensioned, coolant leaking on to them is definitely capable of producing the noise you’re hearing.