All scanners have birdie frequencies, which are signals created inside a scanner that can cause interference.
To find the birdies in your scanner follow these steps:
1. Disconnect the antenna, and make sure that no other nearby radio or TV sets are turned on.
2. Search every frequency range from its lowest frequency to the highest. Occasionally, the searching will stop as if it has found a signal, often without any sound. This is a birdie.
3. Make a list of all the birdies in your scanner for future reference.