Renault Megane 98; whiny, whirring noise?

I have an S plate megane (1998) with 41,000 miles. I have recently started hearing a whirring noise (not coming from engine because the thing idles fine) whenever driving.... When stationery I hear nothing. I have dropped into neutral when driving and will hear the same. So I dont think its the engine. What could be causing it??? Very annoying!!!