Ok , thanks a lot for the help!
During the process I've noticed a 2nd issue-
If I turn the volume all the way up, there's a soft but noticeable high pitch noise coming out of the tetra.
I've checked it on my mopho x4 using the same gear, same instrument cable and power supply and its clean, so the noise is from the tetra output only. Any idea about this? Also tried a different power supply, different socket and different instrument cable, the problem persisted. (I had no usb/midi connected to it)
Thanks again!
Micha