whirring noise autosleeper Sherbourne

At highish speeds and winding we get a strange rattling noise from the drivers side air vent.
Anyone now the cause or the fix ?

So & Debs

Perhaps the ducting has come away from the vent?

Is it definitely from the air vent ? I had a strange noise that I eventually traced as the black plastic trim above the drivers door (between the cab and the overcab). The front of it was starting to come loose and so vibrated when caught by the wind.