Do sounds created by Minor Illusion have to have a single fixed origin point?

Question

The Minor Illusion cantrip lets you create either an image or a sound for one minute. The text gives a variety of explicit and implied restrictions if you create an image, but seems extremely broad if you choose to create a sound.

If you create a sound, its volume can range from a whisper to a scream. It can be your voice, someone else's voice, a lion's roar, a beating of drums, or any other sound you choose. The sound continues unabated throughout the duration, or you can make discrete sounds at different times before the spell ends.

Whereas the image case of Minor Illusion specifies that the image must fit in a 5 foot cube, there is no text dealing specifically with the position in the sound case other than the 30 foot range of the spell. In fact, the text doesn't seem to say that Minor Illusion in sound mode has a target in the usual sense.

1. Do the noises have to sound like they originate at a particular point, or can they seem to just generally pervade the 30 foot range if so desired?
2. If there is an origin point of the sound, does the origin point have to stay fixed throughout the duration, or can different "discrete sounds" originate at different points?
3. Is it possible to create a continuously moving sound within the range, like an illusory conversation that wanders by a guard in a hallway?

Answer 1

You are not restricted to an origin point.

Compare the wording of the Minor Illusion cantrip to the Thaumaturgy cantrip:

Minor Illusion: You create a sound or an image of an object within range that lasts for the duration.

Thaumaturgy: You create an instantaneous sound that originates from a point of your choice within range, such as a rumble of thunder, the cry of a raven, or ominous whispers.

While minor illusion goes into great detail specifying that a visual illusion cannot permeate the full 30ft radius, there is no RAW limitations on the sound's location or lack thereof while in the range.

You cannot, however, have multiple sources of sound. An illusion is limited to a single object unless otherwise specified. You may create a complex chain of discrete sounds as part of the illusion, but it's still one audio illusion.

Lastly, minor illusion's source cannot be moved. Jeremy Crawford has repeatedly confirmed that minor illusion cannot move. He states that illusion spells that were meant to move (mislead, major image) will specify that you can move the spell.

Of course, this is all limitations on the spell. You can manipulate the actual sounds produced by the spell, incorporating echoes and changing the volume of discrete sounds. The DM can decide if your character is a skilled-enough sound engineer to craft a believable illusion, or if these tweaks will have any effect. As Crawford himself says,

There are no D&D rules police, thank goodness. Customize the game in the ways that give your group the most enjoyment.

Answer 2

The spell works as it says it does.

This is a term that's used a lot, but in 5e Specific beats general. So spells that target an area up to 30 feet away unless it says that the spell can move such as silent image or other spells than it doesn't. Unless it says the spell ends when you leave the range it doesn't (witch bolt for example.)

In order to know how far away the sound can be heard, use the sound table on the DM screen. There is no specific text in spell saying that only those within a certain range can hear it.

Unless otherwise stated, somatic components and other components are only performed when you cast the spell.

Generally if you read through a spell a few times and pay attention to where they put grammar, it can help with spells such as minor illusion.
The sound you choose continues. Meaning that whichever one you picked that is the one for the duration. The reason for wanting to ever dismiss it is if you chose when you cast it not to cast it with the discrete sounds.
The sound continues unabated throughout the duration, or you can make discrete sounds at different times before the spell ends. The above statement gives you options. Just like you're choosing visual or sound, your choosing continuous or discrete.

For use in combat, this spell is entirely up to the DM.

This spell doesn't give any added benefits for combat but generally most GMs will try to reward creativity.
Using things like making it sound like shouts from a reinforcement.
Using your voice from one direction while you hide at the other.
There are lots of uses, and if the DM feels that a creature would want to investigate a sound instead of fighting, that is up to them.
Generally minor illusion is an outside-of-combat spell
Things like making it sound like you're in bed snoring when you know people are sneaking into your camp. Making the guards notice some whispering in bushes your not in. Etc.