My first guess would be the power steering or alternator belt. If so, there will be a screech as and when the belt slips. The screech is quite distinctive and it will come and go at different speeds. If it's the power steering belt, the steering may become heavy. If it's the alternator belt, the red battery light may come on intermitantly on the display. Neither are too serious and if you are going to fix it yourself, you should check that both belts are tight, buy a spare (£3 - £10?) and fit it in the next couple of months. If you are using a garage, it will be a 30 minute job if my guess is right. If you do nothing, the noise will get worse and the belt may fail at some point (this would leave you with heavy steering and/or no charge going in to the battery).
Some vehicles have separate rubber belts for the alternator and steering. Some have one belt.