I think you should try to find exactly what is making the noise. Is it from the poly-v belt itself, or is it a whine from one of the pulleys it drives? Squirt some water on the belt while running. If the noise disappears, it's the belt. Inspect it for wear and damage. I cleaned my 16yr old 110,000m Focus belt with a toothbrush bent at rightangles - take care if you try this!

If the noise continues, consider the cambelt. Inspect it for wear and damage. Perhaps the tension pulley is beginning to seize? If so, the back of the belt may show signs of heat damage. If so, change belt and pulley pronto! If not and all looks OK, try the same water test on the cambelt. If the noise goes away, the pulley might be seizing slightly but not enough to damage the belt yet. So change belt and pulley soon.

If still noisy, consider bearings of water pump and aircon compressor.

Please let us know what you find.