Our fridge is about 13 years old (older than any of our grandchildren) and it is struggled this summer. For the last two weeks on closing the door it has whistled at me!
I looked up advice on the internet, It is so useful for this kind of thing.
What was the advice? - clean it basically. It suggests fluff bending fan blades; blocked ducts; ice overload in the automatic de icer; etc. Apparently the fridge pulls the cold air up from the freezer to take them temperature back down when its been opened even for a few seconds.
So I emptied as much as possible, stopped picking any more garden stuff for a day and borrowed some freezer space in a neighbours and started the cleaning inside and promised to vacuum the outside
The whistle stopped!!
Phew - no way can we afford a replacement at the moment!