Carlos
When I first got my PSR2000 I had hissing sounds and some that sounded like rushing water,etc and I even considered taking it in for repair, but I did the following:
did an initial setup by holding down the C6 key (the right most key on the board) and then turning on the power.
The noise was reduced somewhat and the rest of the problem was the fact I always have a mic plugged into the unit and when I started to turn the noise gate on and off and turn the dial associated with the noise gate - all the hiss etc disappeared.
If you don't have a mic plugged into the unit then I don't know what the problem could be.
RR