Is it possible that you are not giving the unit enough signal level ? They typically have about 110dB dynamic range – this means that if you can hear the input noise, full level would be deafening.
What input are you using (XLR/jack balanced/unbalanced) ?
What led meter reading do you get with a typical signal ?
Does it give you this noise with a "Thru" preset ?
Do you get the same noise level with channels 1/2 as 3/4 ?
