Problems with noise in new build house roof

The roof on my new build house suffers from rustling/creaking noises around the eaves area when it is windy. The national house builder has done some remedial work to secure lose timbers in the loft and has taped the overlaps of the roof tile underlay felt but none of this has helped, and they now say there is nothing more they can do. The noises can be heard in the bedrooms and are intrusive. I have attached a file showing the eaves area from inside the loft - is this how it should look and any idea what the white plastic filler is for? Any advice will be appreciated.

 

Yes, it has loads of ventilation - the wind blows through the roof and the black corrugated layer that you can see in the photo is moving in the wind - plus I can see daylight through the eaves.

 

Thanks for the link to channel 4 - interesting programme!