I understand now, Yannis, Thank you.
You are hearing background noise.
You should make sure about the following:
-the unit analog I/O should be properly wired for what is the type of signal you are using, balanced/unbalanced and -20dB instrument level or +4dB line level signals.
-using *studio grade* professional audio balanced shielded cables, such as Canare, Mogami, Belden is greatly recommended, rather than generic guitar/mic cables. These companies make the best cables in the industry and are used to wire professional studios. I use Belden.
The optimal performance (signal/noise ratio – audio clarity – high levels) is obtained with full balanced I/O, running +4dB line level signals. These types of signals are pre_amplified. I have no knowledge of what exactly you feed the unit with and how, but I assume you are using pre_amped sources for +4dB signals.
all the best
I
