"/sdcard/Sounds" folder appears empty in Windows 7 for Samsung Galaxy S3
Being aware it is not a full-fledged solution but rather a workaround (it's still unclear what's causing the underlying issue), this answer sums up what we figured being a work-around at least:
As the files/directories don't show up the usual way via &quot;sharing the SDCard&quot;, they can still be accessed by other means. One example is using ADB: using adb pull files can be transferred from the device to the computer, and with adb push in the other direction. Examples:

adb pull /sdcard/Sounds/ E:\audio\phone would take the entire folder /sdcard/Sounds and save it as E:\audio\phone on the computer
adb push E:\audio\phone /sdcard/Sounds/ for the opposite

The culprit: types of &quot;source&quot; and &quot;target&quot; must match. If &quot;source&quot; is a file, &quot;target&quot; must be a file as well: adb pull /sdcard/Sounds/some.mp3 E:\audio\phone would fail as the source is a file and the target a directory.
Other draw-backs can be worked around as well: if you prefer a graphical solution over tinkering with the command line, there are several good GUIs available, e.g.

QtADB
Droid Explorer (by our member Ryan Conrad)

And several more. As a side-effect of installing ADB, you've got a powerful tool ready which will certainly help you with many other things!
For getting ADB to work without installing the full SDK, please refer to Is there a minimal installation of ADB? More ADB related information can be found via our adb tag and its tag-wiki.
Alternatives include several &quot;WiFi file managers&quot;, which are too many to be listed here. So if you rather want a &quot;simple app installed&quot; on your Android device, and then do everything with your browser, you might wish to take a look at the following lists:

Manage your Android Device from your Computer
FTP Server
Various File Servers