Hello.
I am not sure whether this is a real bug or not but it struck as weird for me.
Exitting the SGS train platform to tne north, middle road to GMS compound, you can descend to a small subway where are several stalker people lurking around. For some odd reason, sound effects sound muffled at certain spots (like one locked gate leading to a combat with three rathounds, there is a dead man inside, and you can usually get a nice armor there too.