A constant low level hissing noise is a normal sound associated with speaker operation. All active speaker amplifiers generate sound which is heard through the speaker elements. This is called self generated noise level, which is <5 dB A or even <3 dB A for latest Genelec products. This is a very low noise level, and most active speakers on the market are not capable of producing such a low noise floor.
In a very quiet room and sitting near the speakers, the normal self-generated noise can be heard when there is no other noise or music in the background.
To reduce the noise level, there are two options: You can either lower the sensitivity using the rotary control on the backside of our speakers (turn it counterclockwise), or with our SAM models, you can adjust the sensitivity using the big fader in GLM. (Note: the rotary control on some of our SAM models is only active if they are not connected to GLM and with the Stored DIP-switch set to OFF.)
If you do this, however, you must keep in mind that you will have to increase the volume of your sound source afterwards and that your sound source may also produce some noise.