check your cables: audio with audio, powercables with powercables & midi cables with midi cables. do not mix up!
disconnect everything and see if the noise is still there. by everything I mean your synths, samplers, FX, mic (!!!), and everything else except your tt & dj mixer
try to get the best cables you can afford. old & cheap cables will give you more noise
check if your dj mixer and tts are still ok
if none of these helped plug your powercables into another plug in the wall. switch, try ... you might fix it
It could be that you simply cant fix it ... means tat your electricity in your house is bad, i dont know much about it but I have that problem here
you can check things by setting up your setup in other rooms