Is it a mod compatibility issue?

Yes

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

https://modrinth.com/mod/sound-physics-remastered

Minecraft version

1.20.1

Describe the issue

I'm playing with the Sound Physics Remastered mod. Before installing Immersive Portals, this error did not occur.

When I am on the surface, in the overworld, I hear the sounds of monsters deep underground. Also, when I started looking for the source of the noise, I noticed that I could hear mobs from above (sheep).

Disabling Sound Physics Remastered fixed the bug, but I decided to try to fine-tune the two mods in relation to each other anyway. And I found a slider in the Immersive Portals settings called Indirect Chunk Loading Radius Cap. Reducing this setting to a minimum limited the draw range through portals, as expected, but also almost eliminated the unwanted sounds of monsters from underground. Accordingly, the increase produced more sounds.

Other settings (including in Sound Physics Remastered) that I tried did not affect the situation in any way.

Steps to reproduce:
1.Turn on Sound Physics Remastered, Immersive Portals and dependencies.
2.Create normal creative world.
3.Build and burn a nether portal.
4.Near, dig down a 40-60 block deep hole, spawn a pillager (for example) here.
5.Name him with a tag.
6.Fill hole with blocks.
7.Now, on the surface you may hear pillager and maybe other mobs that spawn in the caves.

I'm thinking this might be a different kind of incompatibility issue since I also get the same bug without Immersive Portals being installed.

This is definitely an immersive portals issue, although it could be that some other mods cause the same issue.