Squeaking Under Acceleration

Forum: 

Car: Charade 1988 (not 89 as I my name says - typo)

Displacement: 1 L

Problem:

There is a squeaking noise when I accelerate, especially on hill starts after I shift up into gear. This happens mainly in first, though if I accelerate fast then it happens in others.

What could this be?

There is a belt that runs on three pulleys and drives the alternator. Could the belt need replacing?