Don't underestimate the noise produced by the Train as it passes through the commuter rail station. Different trains have different noise levels. Some are relatively quiet while others will rattle your fillings. There is nothing between my place and the elevated platform except air. As a result I have nothing to buffer the noise of the trains as they pass. With the windows down the noise isn't bad. Modern windows dampen sound well. It appears the Engineers make a conscious effort to not ring the train bell too much or at all depending on the number of people on the tracks, weather conditions, unmet need to hear the bell, etc. It's the locomotive itself, however, that's actually loud.
The train noise is a very important detail to consider when purchasing a unit near the tracks, especially the condos in 7 Central, where a corner unit is a mere 25 Ft (estimate) from the tracks. I imagine the walls must vibrate when the train passes. Buildings such as the Boston Machine Lofts and Exchange St. Lofts which are near the tracks but have buffer buildings between them and the tracks needn't worry. Buildings like the Sherry, Keith, Monroe, 31 Munroe, and 7 Central have it a bit tough, especially the two Munroes and 7 Central. The developers of the Munroes designed the units so that there is a big closet and insulation between the wall facing the tracks and the unit interior. I don't think there are windows, so it shouldn't be bad at all. 7 Central will most likely have nothing to attenuate the noise since it's being developed by Mayo Group, which always does things as cheaply as possible, and tends to hire unskilled workers that exacerbate the problem.
The Sherry Lofts poses a mix. There are units that face the tracks, but the Munroe and Pevear buildings sit across the street and between the Sherry and the train; however, there is a large passageway (pretty actually, in an urban way) that leads to the platform from Munroe St. The units that face that passageway from the Sherry will probably get quite a bit of noise. My educated guess.
Most open houses are on the weekend, especially Sunday. Good for scheduling but bad for experiencing what the area is really like when you live here. The train runs more often during the week, and runs the least frequent on Sunday when realtors are showing the properties. You'll have to stick around and time your visit so a train goes by while you're looking at the property to truly appreciate the noise or lack of. I highly encourage you to do this. It will affect your decision, and should you decide to go for it you'll sleep well, even with the train. I'm a very light sleeper. The result of 6 years of military training sleeping on submarines in really sketchy waters. I sleep well. The rain wakes me more often than the train. The train - you get used to it.
Central Square Lynn - walk to the train, walk to the beach. If you don't mind the roar of ocean waves you'll find the train easy to deal with. While I'm thinking about it, I do recommend an eye mask for when the sun comes through those big monster windows. Noise - you can get accustom to - the sun - not a chance. Wakes you every time.