Under a holding stack
When airports are very busy there can be a build-up of planes waiting to land. To make sure there is a safe gap between each plane landing, ATC keeps these planes circling until they can land: this is called a ‘holding stack’.
The minimum height of the holding stack is 7,000 ft above sea level. This means that the noise from the stack shouldn't cause a nuisance. Of course, this can’t always be the case, and people are sometimes disturbed. This happens more often when a holding stack is over the countryside, where there is little background noise, such as road traffic.
Every airport has several holding stacks and Gatwick has two, designated as ‘Willo’ and ‘Timba’.