I particularly love that sound brick from that Agents set with the big fence that the car rams through, and an alarm sounds. That one is so cool.
But I definitely agree, more sound bricks would be aeswionme, animal sounds and fog horn would be great. The one from the Grand Carousel set is indeed also a really cool one, though if I hear it once I can't get that melody out of my head for days.
Between plotting to kill you all and chasing balls of yarn, I also build MOCs