Citroen C3 headlights make squealing noise when switched on.

For the last couple of weeks my headlights have been making a noise, usually a squealing sort of noise (a bit like a belt slipping) and occasionally more of a discordant kind of eeek eeek sound! I took it to my garage today and paid £70 for half an hour of labour and a new belt. The mechanic said I "may" also need the "tensioner" changed or something like that. I drove home, switched the lights on and....nothing has changed! The mechanic told me he had difficulty getting the lights to make a noise but all I know is for the past couple of weeks there is a noise every single time I switch the main beam on (it is possible he only switched it to side lights I suppose). It makes no difference whether the engine is on or off by the way, just turning the light stalk to main beam is what makes the noise start without fail. Help me please! The noise is loud outside the car too by the way and I am afraid of getting stopped if I try to drive it at night the way it is.