slsduque

Hi.
I've been using kx drivers for a long time and I am very happy with the results. I thank the kx community for providing such hi level drivers and mantaining an excelent support for the users.
I have an old 5.1 live board and I'm using Version: 5, 10, 00, 3538 of the driver.
For the first time I connected my system to a 5.1 amp through the 5.1 direct input available.
I configured the surrounder plug in to the 5.1 mode and set surround to 'on'. All ok and I started to change settings looking for a better spatial distribution and a more pleasant tonal characteristic.
So, I went to the ac 97 settings and verified that the 'high' position for the 3dse box was what I was looking for. The sound became clearer with a good sense of spatialization.
Unfortunately, when I turned the player off with the amp still on I verified a unpleasant noise( Hisssssss) coming from the speakers ( at a high level of the volume setting I must say). The level of the noise varied with the choice of the setting for the 3dse:
off=pratically no noise, low= an audible but low hissss, ...., high= situation described above.
Do someone have an idea of what may be causing that noise and a way to eliminate it?
Thanks in advance