Version 1.23 PC offical server
My friend and I where looting. We killed some zombies around 100-200 metres away from us, then went back to our car and continued looting for around 5 minutes. We drove down the road towards where we killed the zombies, and we found a pack of wolves eating the zombies. We never heard any howls. Luckily, I just ran them all over with my car. I don't know if this is a bug or feature, but it's something I noticed anyway.
Maybe, when the wolves spawn and a edible object in within range of them, they never howl?