RMX-1000 & distorted KRK monitor speaker

Hi,

Just got an RMX-1000 connected to the send/return of my DJM-750MK2.

When activating the RMX with the blue button on the DJM and using the scene FX one of my speakers is making huge cracking sounds. It's that severe that I'm afraid to damage them.

The weird part is that it's only 1 speaker. It's not related to the speaker 'cause when I switch speakers the distortion is on the other speaker.

Speakers (KRK) are balanced and connected to the booth outputs. Even tried different cables. Before, they were connected to the master. So I thought the issue was related to the master. But it still happens when connected to the booth.

RMX has the latest firmware installed.

Would be so grateful if somebody could assist to get this solved.