You can see that there are 2 mainstem bronchi in the cranioventral portion of the chest and only one in the dorsocaudal portion. The cranioventral chest is narrower than the dorsocaudal chest. So there are more “noise generating structures” in the cranioventral chest and they are nearer to the chest wall. Et voila! Louder lung sounds! If an animal is taking very shallow breaths then you may not actually hear lung sounds in the dorsocaudal chest. And good luck with purring cats!