Audio decreases on both Chrome and Firefox

When I'm trying to play a video on both Chrome and Firefox, the audio starts getting quieter and quieter until you can barely hear anything. Once I stop the video, I hear something that sounds like a fan running then when I stop hearing it and play the video again, it's fine. The only way to fix this is to stop the video and play again but I keep on having to do it and it's annoying. I notice it happens when the video is playing music. When it's just people talking, it doesn't do it. The audio is fine then. Does this mean anything? I've read about cleaning the inside of the computer to clean the fan but I was wondering if there was a way to clean inside the computer without opening the back. I can't find the vent on this computer. I also tried uninstalling and reinstalling my audio driver but that didn't do the trick. Also updated my graphics driver and that didn't do the trick either. When looking at my device manager, I noticed I got both Realtek HD Audio and AMD HD Audio device. Should I actually be having both on my computer? Maybe this can cause a conflict?

My specs

Anyone?

Just a little update. I tried updating my audio driver. No solution either.

Could be the fan getting pretty dusty. I cannot find the cooling vent on my computer, not even on the back so I can air spray it. Weird.