That is sounds very bad sorry to hear that.
When i read your message my first thought was the unit need to replaced but as I can see you have that problem on both two uTrack24. Very unlikely both two device has this issue…
The only thing came in my mind is that DB25 cable pinout is that cable has Tascam pinout?
Do you hear the same noise where the DB25 disconnected and you listen the TRS output on the back of the uTrack24?