Sounds like it could be Ground Loop Interference.
I suffered incredibly badly with this to the extent that it sounded like the Aliens were landing. I ended up curing it with an ART DTI Dual Transformer/Isolator which cost around £40. If it is Ground Loop Interference there are a great many ways of defeating it depending on your own personal circumstances and you would really have to read up on it and begin a process of trial and error until you find what works in your own specific case - and just because the ART unit worked for me doesn't mean it would for you.
You can read my thread here https://www.propellerheads.se/forum/...ht=ground+loop
Best of luck mate