Whistles / warbles / twittering on FM

This is most commonly caused by weak signals from another FM transmitter interfering with the one you're listening to. This can happen for a variety of reasons; high-pressure weather, tuning to the wrong transmitter for your area, using an aerial which isn't directional enough, or living in an area which isn't well served by FM signals.

Occasionally the problem can be caused by your radio being affected by a transmission other than an FM one. Examples might be a taxi service, a radio amateur or CB operator.


What to do

  • If it only happens during stable, fine weather associated with high pressure, and tends to fade in and out gradually, there is little you can do except wait for the weather to change. This tends to effect stereo more, so switching to mono can sometimes help.
  • If it happens all the time, ensure you are tuned to the best frequency for your area. You may need an external aerial if you are listening in stereo or you are in a difficult location for FM reception. For more information you should consider seeking the advice of a qualified aerial installer because the choice of aerial type can make a big difference to the quality of FM reception.*
  • Whistles caused by breakthrough from a transmission other than an FM one tend to be intermittent, and each period of interference will have a definite start and end (in other words it won't fade in and out). You might even hear voices in the background, which can be distorted. With a portable radio there is normally little you can do, but Hifi tuners can be fitted with filters. Visit this page for more information on filters.  

For help with aerials and dishes we would recommend using a professional installer. We cannot recommend individual installers but you may wish to seek advice from a recognised industry body, such as the Confederation of Aerial Industries (CAI).

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