Something flapping

Some days, not always, when I hit the motorway and drive at about 130 - 140 kph, maybe when it is a bit windy, I hear something flapping at the front.
It sounds as if a rubber hose was slapping the body somewhere in front of the windscreen or something made from rubber flapping in the engine bay and hitting something. Only at those speeds. It is not very loud, but strange. Any ideas what it could be or have you heard anything similar? Could it be the wipers? On some days it does not happen at all. I suspect a bit that it may be when I drive against the wind. Yesterday when I was driving west and it was a west headwind, it did it all the time, on the way back to the east nothing.

Loose undertrays are a favourite; I see loads 'hanging low' as it were...

Daft as it sounds but if you have the window open it could be the seatbelt flapping

I found from the belt at the bottom mount upto the top mount seems to flap when the wind blown thru the window hits it and makes a flapping sound

i would notice that, i don t open windows at that speed

the sound is much more muffled, coming from outside, not inside

i will try to find out about that where panda has undertrays or what it is

thanks for the tip

some plastic flat parts attached to the bottom of the car, ok, lets see

There's no undertrays but it could be the liner between the wheelarch and the engine bay that has come loose.