I would agree that it could simply be the auxiliary belt .I would have the tendency to think that it would maybe need replacement,they dont last that long,probably 2 - 3 years would be it for that belt,thats what i'm finding with mine anyway.They can be a little fiddly to replace depending on the model but the adjustment usually is done by a offset pulley or on the water pump itself.On mine [ an 02 1.9 diesel the adjustment is automatic and is done by a spring loaded pulley so not something that you can adjust.] Perhaps it may pay to get yourself a Haynes Manual ,itll tell you in there for your specific model or if you dont feel confident go into your local [ TRUSTED ] garage and get them to fit a new one.There's lots of different lengths so you will need to know the correct length if you intend to fit one yourself which is usually marked in MM s on the outside of the belt itself and clearly visible.They aren't very expensive and well worth regular replacement.
Which engine do you have?
On the 1.4i Gasoline, there's TWO belts, one for alternator and one for the PAS.
Adjustment for the alternator is easiest reached from the wheel-well, to the rear of the suspension, and the adjustment for the PAS belt is in front of the suspension, close to the edge of the engine block. Kind of fiddly, really as you need to slacken 2 screws holding the tensioner in place before you can start moving it.