very loud interference with Alto live 1604

I have the Alto Live 1604 since some month and having an issues with my unit.
Indeed, from time to time and after a while of working i have a very loud interference coming from my unit.
First i was thinking of a problem with the sources connected to the mixer (synths and external fx processors) but nothing's wrong with my units. This interference is disappearing when i switch off the unit and only if i wait some minutes.
Could it be an issue with the preamp or circuitry?
Of course my live 1604 is still on garantee but i would like to know if you do have a clue about this very strange behavior.
Thanks for your help.
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