People have complained about the loud machine sounds they hear all over the map. They are not belonging to the map. They are played because the dedicated server is having problems with GMod's mounting system making it replacing some HL2 sound files with other games' ones.

This bug is hopefully fixed in the next version of GMod and it doesn't occur in single player nor in listen servers.
Edit: It's still not fixed. It seems to be an issue with EP2.

Try to disable the sounds by entering "sv_map_soundscapes 0" in the server (via rcon, if in-game) console. If this doesn't work, this might help: Override the scripts/soundscapes_gm_construct_flatgrass_v6-2.txt file by an empty one and force download it to the clients. (Edit: See below)

If you hear some wind outside, some water splashing near waters, some quietly noises inside and some stormy wind in high areas in the sky then everything is fine.

Edit:
The latest update mutes the soundscape on dedicated server. If you still hear these sounds make sure you install/run included the lua script lua on the server.