Ground loop causing electrical noise/interference

Electrical noise or interference (buzzing through speakers, weird meter readings, ghost triggering on sensors) is a classic sign of a ground loop — multiple ground paths creating a small voltage difference that shows up as noise. These are genuinely tricky to trace since the fix is usually about consolidating grounds to a single point rather than finding one broken wire. What symptoms are you actually seeing — audio noise, meter readings, or something else acting up?