On a recent IFR lesson the tower radio had some sort of failure. When nobody was talking, there was a loud alarm sounding on the frequency. When I talked on the radio, or the tower answered, it went away. This happened while shooting an ILS. Communication with the instructor was impossible. I was glad when we went missed and were handed to departure, the noise stopped. Took them about 10 minutes to sort out whatever it was.
-- IFMU