When using the latest lwjgl the sounds for pistons extending are missing. All the other sounds seem okay just the piston ones.
Comments 3
Maybe that soundfile is corrupt.
Redownload the sounds by pressing F3 + R ingame.
If that won't help, start Minecraft by the following batch file
minecraft.bat
java -Xmx1g -Xms512M -cp minecraft.exe net.minecraft.LauncherFrame
pauseand look in the console if there are some messages when trying to play the piston sound.
Nevertheless, this is no minecraft bug.
Try downgrading to version 2.8.4. The most recent one has been known to cause issues with minecraft.