What is used to suppress radio frequency interference from a line-driven AC motor?
Why Brush arcing in an AC motor makes broadband RF hash that rides out of the motor on its power leads and radiates from the house wiring. A brute-force AC-line filter is a heavy-duty low-pass LC network rated for the full line current, inserted in series with those leads so 60 Hz passes freely while RF energy is shunted and blocked at the source. Killing the noise where it is generated is far more effective than trying to filter it at the receiver.
Watch out The high-pass filter answer is exactly backwards: a high-pass network would pass the RF hash and choke off the 60 Hz power the motor needs. Note also that a bypass capacitor by definition goes in parallel (shunt) to ground, not in series, so that choice describes an impossible connection.
Brute force = low pass: let 60 Hz through, keep RF in. Filter the noise at the motor, not at the radio.