how to check if the entity is making a sound

Thats a neat part, you can't (unles you do it proceduraly).

Maybe try using those procedure triggers and make it feel like entity checking sounds.

For example for walking you can try checking if entity is on ground and [fast enough]/[crouching] to make step sounds and then sending informations to entity by modyfing entity's custom nbt (and some global entity variables if you want to have for example target). And for your warden like entity make update tick procedure that sets his target based on his custom nbt (and global entity varable (target entity)).

And you could improve 'example' above by using array(s) to save previous sounds and remove them after while.