I'll try and explain this clearly!

I made some new idle sounds, and made a new sound descriptor package to contain them, containing sqeaks, nibbling, and other rat-like sounds for the Skeever. All previews of the descriptor work fine in the CK, etc. The sounds for the breathing (Conscious Loop) are defined in AudioTemplateSkeever NPC template, which is inherited by EncSkeever. This is a typical model for all creatures so variants can share the same sound set. Idles and breathing sounds are always defined here, specified by type.

In the Actor Sound Data of the NPC template, I added my new sound descriptor, and set the type to 'Idle'. I used the Mudcrab as reference for how this is set up.

However, in game, the Skeever never plays any idle sounds, no matter what it's doing.

As a test, I changed the type from Idle to Conscious Loop for my sound set, to replace the breathing, and it plays fine (constantly looping squeaks, not the result I want of course) which showed me that the sound descriptor and sounds are not the issue.

It looks to me as if the Skeever idles do not have any sound associated with them, and as such never trigger the Idle sounds defined in the NPC/Actor Sound Data. However, I cannot find where idle sounds are defined, after a couple of hours digging. For creatures, Death and Attack sounds are defined in a base Dialog quest, but idles are not.

Any help would be greatly appreciated. Thank you!

If you cannot find this (I took a fast look myself with the search tool in the CK using "IDLE") You could just play the sound effect from a magic effect / script that is conditioned for the activity of idling (no combat, not running and other things like that).

You may not need even need any script as spells can have sounds. Make a null magic effect were the only purpose of it is to play the sound. Then attache the spell to the actor race.