Hearing noise in a balanced system

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Hello,

I have a Hypex based 6 channel set up: Digione--> Hypex DLCP --> 6 channel Hypex UCD amp --> Linkwitz Studio.

Yesterday I heard some sort of noise, a kind of hum, about 120 hz through the speakers. (Power supply voltage is 240)

This is a fully balanced kit. Wiring is as per Hypex recommendation, ie for each channel, shield cable from dlcp board goes to DLCP end XLR pin 1 --> Amp chassis XLR pin 1 --> Ucd amp board signal ground pin. XLR pin 1s are shorted to chassis at both sides.

I use Hypex interconnects between the DLCP board and the Hypex Amp chassis.

Technically, I shouldn't hear any noise or hum right? Where could theory be going wrong, then?

Advice welcome.
 
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