Sound in Dreams

I had a vivid, non-lucid dream this morning that involved me riding in the back of a SUV whilst defending against zombies with a MP5 machine gun. The gun itself was pretty realistic (as was the rest of the dream), and I had the opportunity to fire it at some lawless bandits who were shooting at our vehicle.

I had to fire it through the window and the bullets went through them as expected, although the window never completely shattered or broke down.

One noticeable thing that was missing was the sound of gunfire, however.

Now, I was talking to the person driving the vehicle and I can clearly recall "hearing" my own voice, as well as his, as we were racing down a dirt road. I just didn't hear any sound coming from the gun as it fired and there was no dream-silencer attached to it.

Aside from this being a clear dreamsign that I could have used to become lucid (along with the fact that we were running from zombies), I have to wonder why some sounds are so conspicuously missing in many of the dreams that I have. I guess that all it means to me, practically speaking, is that I have a clear dreamsign that I can use to become lucid in future dreams.

If there is no sound, it might be a dream.