Most expensive radios have a squelch knob, especially Ham Radios and CB Radios. You adjust the squelch knob until the static and background noise is turned off (basically turning the speaker off for low signals). When a higher powered signal is received, it has enough energy to break through the squelch so you can hear the transmission. The squelch should be set just at the point where the speaker is silenced for best use. If you are listening for a weak-signal source, turn the squelch all the way off. The hiss and noise will drive you nuts while you strain to hear the weak signal, but it's the only way you'll be able to hear it.