Does the fade in and out occur during music streaming or playing local files or both?

Does it occur on built-in speakers or headphones or both?

If you are using bluetooth headphones, do you have another bluetooth device attached?

What software are you using to play the music?

Are you downloading anything (other than streaming the music file) while playing music? https://discussions.apple.com/thread/2512262?start=0&tstart=0 indicates downloading music from iTunes while playing other music (even local files) will cause a fade in and out behavior. Other downloads of files or email could possibly contribute to the problem.

Do you have an Atheros Wireless Network Adapter? If so, have you updated the driver to version 9.2.1.432 or later? Earlier versisons have DPC Latency, which may be contributing to your problem. Also download and install DPC Latency Checker. There may be other drivers on your system causing DPC Latency.

This is for local files, I use WMP or VLC, the fading is same, I use FLAC and 320Kbps MP3. My headphones are Koss Portapros, JVC HaRX900, and Grado Sr80, nothing that requires an insane amount of power. It doesn't happen with the built in speakers, just when I run it from the headphone jack. I've tried different amps like my Cmoys and Fiio E5. My external speakers are Klipsch Pro Media. Like I said, the problem gets worse with bass almost as if the built in amp is being starved of power. I just can't figure it out.

EDIT: After updating this post, it is probably best to try the recommendations from the bottom paragraphs up.

Did you update your WiFi driver? Not for streaming, but to eliminate DPC Latency which may be affecting local file playback in this case.

What was the results from the DPC Latency Checker? Does the fading correspond with hgh latency spikes? If so, you'll need to troubleshoot by disabling drivers as discussed on the software's web site.

Are you using any other Sound Enhancing software besides the Realtek Audio driver? Since you report an equalizer in the Realtek HD Audio Manager, I imagine you've uninstalled the Creative THX TruStudio application, but I'm wondering if remnants of that app remain and may be causing your problem? I'm unsure what ASUS installs on the G53SW systems, so this paragraph may be irrelevant.

In the http://www.asusrog.com/forums/showthread.php?1150-G73-74-53-Series-Driver-and-Application-Reference Sticky, I see SW systems have a "Creative THX MUI 1.02 Package". Is this installed on your system? If so, does disabling or uninstalling it resolve this issue? If you have an earlier version of this Package, does upgrading to the 1.02 version resolve your issue?

If you go into Sound Properties, right-click on Speakers and choose "Properties" from the popup menu, and select the "Enhancements" tab, is the "Loudness Equalization" checkbox checked? If so, UNcheck it. You could also try checking the "Disable all sound effects" checkbox.

I'm puzzled that the fading in and out is not reproduced by the built-in speakers, unless they are just unable to reproduce the subtle effect. I wonder if it could be an audio jack grounding issue or you are not getting a good contact at the jack? If you wiggle the headphone jack slightly when it is plugged in, does it affect the sound quality?

Here is another suggestion from http://answers.microsoft.com/en-us/windows/forum/windows_7-sound/automatic-volume-leveling-during-au...

1. Go to the sound icon on the system tray, right-click, and click Sounds;

2. Click on the Communications tab. On this one, you will see:

Windows can automatically adjust the volume of different sounds when you are using your PC to place or receive telephone calls.

When Windows detects communications activity:

o Mute all other sounds o Reduce the volume of other sounds by 80%

o Reduce the volume of other sounds by 50%

o Do nothing

3. Select "Do Nothing", then try and check if it works.

It sounds like this wouldn't apply unless you use Windows to make phone calls, but give it a try for troubleshooting purposes. At least 2 other people indicate this settings change resolved their "volume fade in and out" issue.

The above-referenced thread is quite lengthy and may offer other potential solutions if you read through it completely.

I am not exactly sure how I am supposed to read the latency checker. I have been running it for about 20 minutes now and if I am just idling, it goes almost steady green across the board which I think means it's fine. When I run anything like a window or firefox the bars are are steadily red hovering between 3000 and 3500, no spikes, just steady stream of red. Is that good? And I don't have the THX software just the REaltek HD Audio Manager.
I think maybe the audio does fade in and out during speaker playback, but it may just be too hard to discern. Another interesting little thing that I have discovered is that when I watch video wmp or vlc, the video appears to go slightly blurry in a fade in, fade out way. Kind of like a camera continually going out of focus and then re-focusing. I can't figure it out!!

Fortunately and unfortunately I found the driver causing the problem, it's the Nividia driver for my GTX 460m. I have the latest driver that I got from here, maybe I need to roll it back to a previous version.

Update: I went to 285.79 from 285.67 and the latency has gotten slightly better, but now the latency is sporadic instead of a constant latency problem. Maybe I'm not treading it properly, but it should be green across the board right, which indicates no latency issues?

Which version was that? It's not often that a video driver effects the sound system . . .

I was on 285.67 and went to 285.79