I was on the motorway a couple of days ago in my 2012 4.4 TDV8 and it was a very hot day. Having done around 80miles at motorway speed, the car starting making a reasonably loud howling noise from what sounded like the lower, frontal area. It stopped when dropping below (say) 50mph, but above that it started up again. It wasn't present all the time, but for long periods it was.

I looked underneath on arrival and couldn't see anything flapping around and it didn't do it on the return journey today, in cooler temperatures.

The car has been fully serviced within the last 3,000miles, including a gearbox service/flush.

Does anyone have any idea what could have caused this, or was it just a strange frequency/wind noise?

Thanks,
James