There have been many instances where I hear a very grand gong sound while looking around mostly after killing a high level character. It is like a gong of victory or a gong of texture design appreciation. It could also be an indication that something valuable is nearby, but all I've found are some discarded bones. So what is this sound all about?

You're not talking about level-up or word-of-power notifications? When Necromancers raise a corpse there's a chinking sound.

The sound when you "clear" an area/dungeon?

I know exactly what gong you mean, and I'm not 100% sure either. For me it usually indicates I've just cleared a dungeon, or when I'm on the overworld that I'm near a treasure chest..... from my experiences.

There are different sound effects, one of which is for clearing an area of enemies, thats what your hearing.

Also when you discover some dungeons, usually Barrows, there is such a sound effect.

I've had a similar experience. I was clearing out a bandit camp and after defeating one of the enemies, I started hearing the sound you hear when nearing Nirnroot. It wasn't as prominent, but it centered around one of the bandits. After moving the body, the sound still came from it, yet it held nothing important or anything else, for that matter.

clearing and discovering places will make that sound occur

I'm so glad you asked this question because I've been wondering about it too. The answer that sounds right for the situation I hear it is the clearing of an area. Next time I do that, I'll listen for the sound. Thanks!

I've heard it inside of a dungeon I haven't cleared when I stumble upon a "hidden" treasure stash. I usually hear it after defeating the dungeon boss, but that's probably because you're right next to the treasure at the end.