If you create the configuration in the pic below, every time you give the smallest lava block an update, it will make a hissing noise.
If you create the configuration in the pic below, every time you give the smallest lava block an update, it will make a hissing noise.
This is intentional. When Water touches Lava, it always creates a hissing sound.
Unless your saying it keeps doing it without user interaction, this isn't a bug.