How irritating depends on individual...after awhile, any noise becomes 'white' noise and you stop noticing. If a track runs in your backyard, there is definitely going to be a reduction in price, sometimes even up to 10%. But then, you must be getting it at a discount also. You get what you pay for.
I would say that being near a train line might be equal to being on a busy road which generally will decrease market value by 5-7%. So if you have two identical homes, one in a neighborhood and another near a train line or on a busy road I would expect that home to sell for 5-7% less. Still a great home and a great question. From home owners I have interviewed who live along train lines they all say it becomes a white noise in the back ground over time. Best and if you need any assistance please contact.
The fact that you are considering Newton tells me that you already know what a wonderful community it is. Newton also enjoys an everpresent stable real estate market. One of its MANY attractions is its close proximity to Boston...via personal automobile or public transportation.
The fact of the matter is, if you live in Newton, you are going to be NEAR...and HEAR...the train. It doesn't keep people away though! If that is something that will irritate YOU, you may want to consider a different community altogether.
If you're 4 lots away, you definitely will hear the train. Key is- how often does it come and go- and how early and how late? My guess is it starts running around 6:30 am or so and the last train coming in would be about 12:30am- ?? That can be tough, especially if you have an infant who has a hard time getting or staying asleep.
Windows and doors are the key do blocking much of that noise from entering your home. You can actually upgrade you windows to take care of some of this problem.
Other than that, yes- it would limit the price/value of the home to some extent. Tough to put a number on, but I'd say maybe 4%-5% less than another similar home 1 mile away.
If I can be of any help, please let me know. Thanks, and good luck,