So i recently changed over from optical to USB audio through a sabaj a3 amp ive been using for my monitor audio radius 90 and ive only just noticed that when theres nothing playing theres a slight buzz/static noise coming from the speakers. Is this interference because im using USB to connect to my PC?
It's probably coming from the amp you have not the speakers. A higher quality amp should fix thing if it bugs you. Many of the cheaper amps and powered speakers have low level noise, it's pretty much normal.
Some people have tried using a ground loop isolator and it fixed the issue for them