Old beta sounds are being replaced by the new sounds. And spawn rate of mobs have decreased.

When you downgrade to Beta some of the old sounds aren't being used, but instead the new ones are being used.

sounds:

• TNT/Creeper explosion

• Door opening and closing

• Bow firing

• Flint and steel click

• Throwing Snow ball/Egg

And I've noticed the spawn rate of mobs have decreased compared to what it used to be.