engine noise - help to diagnose

[jonp]

I have a 1.8 petrol Ford Focus which has 78k miles.

Since the car had a service last November I have noticed that when the engine is such that it is running at about 1500rpm e.g. at 30mph in fourth gear or 20-25 mph in third gear there is a noise that I can't remember being there before the service - perhaps a coincidence ?

Anyway, I describe the noise as being like a droning sound but like I said only when the engine speed is about 1500rpm. I went to my Ford garage today and he went out with me for a drive to try and see if he could hear the noise. While he was driving the car he acknowledged that there was a droning noise but that it was nothing to worry about and that it may be coming from the gearbox. So I then said could it be a worn bearing or something serious but he said no.

What's your opinion on this and how do I know if the noise is from the exhaust system ?

Thanks