Siotehcat, you sound like you are an extremely considerate neighbour. Hope your neighbour appreciates this fact.
My thought is: can you hear your neighbour at all and what are they doing? eg: talking, vacuuming, music. What you can hear of them will give you a clue how loudly they will hear your sewing machine.
I would not go out of my way to advise neighbour, unless you intend on sewing for hours, and worrying that this will annoy neighbour, I would only bring up the subject next time I saw them outside.
As an example, my son plays bass guitar and I ask him to only practice/play for approx 1 hour at at time and definitely to keep the volume down. (His band hires a soundproof venue for full blown rehearsals...and I am happy about that !!!) My neighbours, when asked, tell me that they are fine with his playing habits, but I always let them know that they must tell me if he plays too loud and long, when I am not home.
So, by my experience it pays to let neighbours know you won't be offended if they let you know to sew less often.