Arco Iris is behind the Argentinian Grille. So you'd likely get a little noise from that. But most of the property is a little farther away. So it's probably pretty quiet. The main road along Half Moon Bay is just on the other side of the Grille. Sundowners bar is just across the street and Woody's Market is about 100' away - it's the better of the two West End markets. Coconut Tree Divers is a short walk the other way. I recommend them, they're fun and very accommodating. The "busier" part of the West End starts past CTD. So it's quieter in the Arco Iris area.
We rented a house just a little west of Posada Los Orchideas. So walked it every day/night after dinner. It's dark but there are house lights and also lights along the path owned by the various properties. I took a flashlight but didn't use it after the 1st night. There's also a cut-through to that isn't shown on the map, once you find it, it shortens the walk slightly. It is a good 5-10 min. walk to PLO though, not 150' as they claim. It's really quiet out there, all you hear are the waves and occasional rain forest noise. Unless the power fails then you hear the generators slightly.
I had no hesitation about walking it at night, most times you didn't even pass anyone. We did have a permanent watchman provided by our property mgr., he mostly made sure the generator stayed on and that our stuff stayed put. So there might be a little crime in that area - saw no actual indication of it though.