Hi all!

I am currently looking around for a used Ford Fiesta. One of the ones I'm interested in is a 2006 Ford Fiesta Zetec 1.4 Diesel. When I took it for a test drive I could here a whirring noise from the engine when travelling at slow speeds. Is this normal for cars of this type? A friend of mine (who is not a mechanic) suggested it could be a problem with the timing belt. Other than this it seems to be in good condition and has 37000 miles on it. I quite like this particular car, but just concerned about this noise. Not sure if it could lead to major problems further down the line. I would be grateful for any advice.