LG G3 :: Unstable System Volume Lowers By Itself

My 32gb LG G3 D855 just keeps on lowering the volume by itself. My touch feedback sound is on and just a notch away from full volume. However, the sound is unstable in that it just lowers itself. I keep checking the setting but the level is just the same and not changing.

For example, one series of tapping on the screen has the expected volume. After some time, the next series of tapping on the screen has their sound feedback dropped by itself to very low. It is fluctuating and unstable.

Just now, I turned everything to full volume and tested things out. To my surprise, even my notification and ringtone volumes are also unstable. They go very low to hear at one point, then get back to being loud again. All by themselves. It came to a point where my ringtone is at maximum level, then when I tested it (tapped at the adjuster), the sound was very low. Then after testing again, it goes back to the intended full volume.

In summary, the volume just drops down by itself, then gets back to the expected level, then drops down again. Very unstable.