I have an older, but functional laptop running Windows 10 that I needed to use to run OBS and record DJ mixes (using Audacity) while using my Macbook for Serato.
However, it was giving off a low scribble sound in OBS and was driving me mad. I discovered that my three-pin laptop charger was causing a ground loop. Took a punt on this and saved me from buying a new laptop. Problem solved!