307 HDI gearbox noise??

Had to go to Bristol area yesterday, and had left some roof bars on the top. When I got there it was windy, and I heard a lot of noise like the wind whistling past the bars, so I took them off. Sadly the noise continued. In the end, at around 40 odd, it sounded like the noise you got as a child when you tied a bit of cardboard to the cycle frame so that it made a noise in the spokes. This is totally connected to road speed, no change whatever gear, whether driving, or on over-run, or even freewheeling down hill. It seemed to be coming from in front of me, or rather in front of my feet. That heavier burring noise has now reduced, but there is still a metallic whine. Just about to have a look underneath, could be a wheel bearing, ot perhaps the driveshaft intermediate bearing (this is RHD car). But of course it could be in the differential. And there was I, booked on a ferry to France tomorrow night. The only good thing, I drove back last night at 55mph, about 20yds behind a large truck, and averaged about 80mpg. Brian.