If your machine uses compressed air, as most do, your max noise level will be Swiss+Air Compressor. The piston-type compressor coming on and off is more annoying than anything, we have a rotary screw compressor that had some of the lowest noise ratings we could find. We planned to have it in the same building as our machines, but quickly moved it out due to the noise and cycling.
It's all about your process too, we have a job that uses max spindle speed and air lines to control chips. That can be heard across the street easily. Then we have a job that uses about live tools with the spindle stopped for most of the cycle and is nearly silent.
I would not want to be in a garage in a suburban development, but if you have some room between your (friendly) neighbors, you'd probably be fine.