Hissing noise coming from light fixture
This noise is not from the bulb, it is from the LED driver. Each LED driver (it is a small circuit board usually inside the bulb, sometimes also called LED ballast) has an inductor inside (bunch of wire wound on a ferrite core). During operation, the current via this inductor rapidly appears and disappears. If the circuit is using cheap parts or is improperly designed, this may cause noise (see http://en.wikipedia.org/wiki/Coil_noise for more details).

The core problem is that your driver is not good enough -- maybe engineer made a mistake, maybe the factory did not put enough epoxy on the coils. The only easy way to fix it to to replace the driver.

There is a small chance that your problem is incompatibility between the dimmer and the driver, but in this case noise should disappear as you turn the brightness to maximum.