Still present in 1.8.7.
It seems like you're speaking of the cave ambient sounds. This is normal, and I don't see how this is a bug. If the sounds annoy you, feel free to turn down the volume.
Try updating to Java 8 and see if the problem persists.
That's why I posted this, I realized it and had to stop the project that you can see in the background of the picture for the moment.
Well, if you do /summon Cow ~ ~ ~ {NoAI:1}, you can still damage the cow. It doesn't react or get knocked back, but it is still hurt and can get killed. So it seems like this would be intended.
Mobs can still take damage even when NoAI is enabled, so wouldn't this be intended?
This is intended, isn't it? Beacon lasers go through all transparent blocks.
Make sure the redstone you connect the command block to is actually toggling. It might be going between power levels 1 and 15, which is normal activity. Try dragging the redstone a couple blocks away from the clock.
Ah, I didn't see that one. Mine should be marked as a duplicate of MC-82896.