Proximity voice chat from Gmod's sv_alltalk 2 can be heard around the origin point of the map?

I have a map based on rp_downtown_v2_v4c running on my server. When people talk near some areas of the map, they can be heard in that area as well as at the origin point of the map. This issue seems to occur with many modifications of rp_downtown_v2_v4c, and I’m unsure of how to fix it. I’m relatively certain it’s a map issue, and this is my edit (so I have the .vmf), but I don’t know how I would go about fixing this. Any ideas?