"We're sort of walking around the house and we're like: 'God, it's a nice day.'

And then we go: 'Oh my God! It must be track work; I haven't heard a train all day," Gracie, a resident of Wollstonecraft, said.

Gracie rents a fourth-floor apartment facing an arched stretch of rail track between Wollstonecraft and Waverton notorious for "wheel squeal" - a loud, screeching noise train wheels make as they negotiate curves.

In a rare intervention, the NSW Environment Protection Authority (EPA) was prompted to act after complaints about the noise from residents in the area. It has now placed a "Pollution Reduction Program" order on Sydney Trains to investigate both wheel squeal and "flanging", which it said occurs when the flange of the wheel rubs against the face of the rail.

"Noise is the primary environmental issue associated with the rail network in NSW," an EPA spokeswoman said.

"Some of the trains are all right," Gracie, who did not wish to use her surname, said. "But some of them are really, really, really squeaky.

"You just have to turn the television off - like mute it - if you're watching a movie and then you have to re-start it because you can't hear anything."

She said she was a heavy sleeper and was not personally fussed by the noise, but her flatmate wore ear plugs at night in order to  sleep.

And conversation was often interrupted by the squealing, she said. "You just stop and start again.

"We're not angry about, we're fine. But it is loud."

For the first time earlier this year, NSW residents became eligible to apply for a share of a $50 million funding pool to help them insulate their homes from the noise, including wheel squeal, of rail freight trains.

But the problems along the rail corridor in Sydney's lower North Shore apply to much more frequent passenger trains and residents there are not eligible for the scheme.

"The newer ones [trains] seem worse, I think," Jeff Parks, a long-term resident along the train line, said. He said he had to shut his door to hear the television.

Like Gracie, April McKillop is acutely aware of wheel squeal, but accepts it as part of living in a big city.

"Noise pollution, yeah, it does get people quite annoyed, but I've lived in cities for quite a long time, so I'm used to headphones, ear phones," she said.

When Fairfax Media visited the area on Tuesday morning, a handheld digital decibel meter beside the tracks recorded trains screeching at above 80 A-weighted decibels.

For comparison, the World Health Organisation (WHO) guidelines for community noise recommend less than 30 A-weighted decibels in bedrooms during the night for a sleep of good quality and less than 35 in classrooms.

Sydney Trains said it was already working to reduce "wheel squeal" at Wollstonecraft and Waverton.

"Steps we have taken include implementing a successful horn reduction initiative and applying special lubricants to the track to reduce wheel noise," a spokeswoman said.

"We carry out regular inspections of that track and complete any smoothing or resurfacing work required."

Sydney Trains has until mid-2016 to complete its investigation into the problem and report back to the EPA.