AM radio static when ignition is switched on.

A distinct buzzing noies which rises and falls with engine speed and is worse with AM reception is usually the result of either a bad radio ground or worn spark plug wires. Make sure the radio is properly grounded and check the antenna to make sure there is no corrosion causing a loss of ground. If all grounds seem good, question the engine's ignition system. Most likely the noise is from worn plug wires causing an electrostatic interference.