And check for loose strands of wire loose strands love AM, or vice versa. Keeping cable runs as short as possible, and cables in well maintained condition, will help a lot. Also make sure you have a decent ground on all your equipment. Over near where I live we have " The 50,000
watt Blowtorch of the
Pacific Northwest, KEX" everyone in the area with old grounds, and old wiring starts picking up KEX on the phone, intercoms, plumbing..........