Hey Jay,..
hiss reason
A hiss coming from powered speakers is not necessarily normal, and it could be caused by a variety of factors. It may be due to interference from other equipment, ground loops, or faulty cables. It could also be an issue with the mixer itself, such as a faulty preamp or power supply.
Elimination of hiss.
To eliminate or lessen the hiss, it is recommended to troubleshoot the system by checking cables and connections, experimenting with different grounding configurations, and isolating the source of the interference.
Shahan