Hello Fabio, the rattling is ok, and as far as I remember, the behaviour was different depending on the range. Either the circuitry simply discharged the caps (rattling sound), or it even shut off the output completely, as if a short circuit occured. This is described in the manual, which you can find on the net. On your unit, I suspect the crowbar driver circuitry and/or sink supply to work incorrectly. Frank