When you collect a pickup, the sound that plays tends to vary in volume depending on where it’s placed in the map (sometimes it’s loud, quiet, or inaudible), which I think is because the sound plays from a static point in the map rather than wherever you collected the pickup.
For example, in Frostbite, pickup sounds are louder near the central Comm Center building, but as you collect pickups further away from it they get gradually quieter until you can’t hear them at all.