Hi Jonezy welcome to the forum, have you done any research on the net
My husband had a problem with his Captivia the sister car to the Antara he was loosing power and the revs would go down, sometime she would hear a whooshing sound, car was only 18 months old so took it to the garage they checked it and it was the turbo pipe had loosened as the clip had snapped in two, they had to order it as it was a single unit once fixed everything was back to normal, might be that
My husband had a problem with his Captivia the sister car to the Antara he was loosing power and the revs would go down, sometime she would hear a whooshing sound, car was only 18 months old so took it to the garage they checked it and it was the turbo pipe had loosened as the clip had snapped in two, they had to order it as it was a single unit once fixed everything was back to normal, might be that