There was previously a bug that caused Lil' XT's sounds to be sent out to a much wider range than they were supposed to be heard. When a few dozen people have them out it can get quite annoying. There's now a hotfix that disables some of these sounds. It's not a complete solution, but it's better than turning off sounds all together.
Vaneras is an EU community manager, and we're not sure if the hotfix is active in the US. However, if it's not in the US right now I'm sure it will be soon.
A hotfix was recently applied, which temporarily disabled some of the sounds Lil' XT makes.
The issue was that some of his sounds were flagged in such a way that they play for everyone around him and not just the player that owns the pet, an annoying problem to be sure. We can't alter volume or who the sounds play for through a hotfix so the temporary workaround is to disable them completely right now until the proper fix can be patched in later.