EXACT same thing just started happening to mine as well: https://youtu.be/ilPGX_fvgBA
This topic seems to be regarding the same issue: Really bad buzzing/crackling sound when turned on
Same thing here: Sound Interference X1800 Mixer No response from Denon DJ
And here…x1800 sound is glitching heavily - any advice? - #16 by Zuckr
Here too… X1800 Buzzing Problem (again)
This keeps going 
https://community.enginedj.com/t/x1800-making-whirring-clicking-sounds/19282
https://community.enginedj.com/t/mixer-making-sounds-and-audio-dropout/8767