Mine started making a noise after about 4 months but only in cold conditions at first. Garage will be able to check the tension for you - had mine adjusted an is now fine But it was when cold which does happen with new belts sometimes.
When the bonnet is up and the engine is running, are you able to hear where it is coming from. Could it be one of the rollers? I know on cambelts they recommend changing the rollers and tensioners sometimes not sure about zeds and the aux belts. But it may point towards a cause.