I've been attacked twice by wolves without them howling beforehand while playing on an official US server. The first time I was walking through the woods, the second through a field. Both times I was in proximity to a military camp (the camps east of Gorka and north of Novy Lug) and I had an item in my hands (an SSG 82 and a backpack). I have heard the wolves howl since I started playing 1.21 so I know they can, but they were hunting another player and a good distance away from me when I heard them.