Question: This is the weirdest issue I've ever encountered with my PC. Every so often, my sound will start playing back at a lower volume. This happens when watching video, listening to music, all independently.

It usually lasts anywhere up to a minute, after which it will turn up again.

The weird thing about it is that the volume control in Windows remains at 100%, even though the volume is audibly a lot lower. (No, I'm not going deaf, it's just my PC. I checked.)

I just have no idea where to go to troubleshoot this, even.

I'm using Windows 7 64-bit with an on-board Realtek sound-card.

Oh, just in case someone finds this question on Google or whatever, making sure this is on Do Nothing may fix your problem. Unfortunately, it did not work for me.

![Windows Sound dialog](https://i.stack.imgur.com/vwEgV.png)

My settings all seem fine. This is my audio slider. (Took the screenshot while the issue showed.)

![enter image description here](https://i.stack.imgur.com/1AHLD.png)

Answer: 
It could be a Steam setting that lowers your system volume when you get a message. 

Turn it off in your Steam settings.
Might be due to your codec pack (i.e. the ffdshow audio decoder which comes with K-lite) settings which are independent from your Windows 7 audio. 

See if there are any icons appearing in addition to the already existing ones on your Windows taskbar during music/video playback. These should be related to your audio codecs installed on your PC.

If yes, right-click on the blue icon (for ffdshow audio decoder) and point to Settings or Options. From there look for Audio settings and try to increase the audio bars as much as possible or until the audio for the played file equalizes in volume to your default Windows volume. 

![enter image description here](https://i.stack.imgur.com/ZLMqs.jpg)

The next time you play music or video files, the audio should be equalized to your default Windows volume.

You can also access these settings when playback is not running by going to Start > K-Lite > Configuration > "ffdshow audio decoder"