Brand new fridge with a fault and technicians not knowing what they are doing.

I have a fridge still in its warranty period. In fact the problem started occurring within 1 month of having bought it. i have had two visits during which 2 separate parts were replaced. Both technicians heard the sound it was making. In both cases the sound started again with in 2 hours of their departure. On a third visit (during which I was not present) they apparently tinkered around and said everything is normal. I have been waiting for another visit. I feel like I am being treated like an idiot - I know the noises a fridge should or should not be making. I feel like they are employing a delaying action as I am now demanding the fridge be replaced.