I'd like to have a pack of wolves in a cave that didn't announce their presence to the player every time he enters the cell. Anyone looked into this? How hard would it be to do that?

you want them to be all silent? then you can just set their noise level to silent in the base item's sound tab.
or if you want them to ignore the player, maybe checking "no combat alert" in their package would do (or making them non-hostile anyhow, depending on what exactly you want to do)

I want them to behave normally and I wouldn't want to silence them completely, I'm assuming that would be weird in combat. I'd need to disable that specific houl that happens when the player gets close, before the wolves actually detect the player.

"npc_wolf_howl_01" is the file I think you're talking about - you could extract this from the Skyrim sounds bsa and adjust the level to be mute (or almost mute) in something like Audacity (or just replace it with a silent file with the same name)...that way the aggro radius won't be changed.