2006 Peugeot Partner whirring noise while cruising

At first I thought it was just the road surface I was on, but it is happening all the time now. Steady revolving noise, rising and falling like a wheel going round, while cruising at any speed with no gear changing, accelerating or braking. Car has only 43,500 miles on the clock, regularly serviced and no problems in the past. I don't have a picture of her but what she loses on looks she more than makes up for in reliability and performance.