After having some sound equipment put in the Council replied saying that recordings show noise levels below World Health Organisation limits. It was said that this was because background noise levels where I live were so low the noise stands out more.
WHO levels are largely irrelevant in defining nuisance. There is even case law that rejects them (and other standards) as a standard for nuisance. The fact that the background is low (does he mean “ambient”?) may even be more of a reason to consider it as a nuisance. Councils still have a duty to investigate and serve notices. In most cases that involves them coming out and listening themselves. Ideally, officers need to get out there on site and experience the noise themselves before coming to a judgement.