The tone is called "DTMF" (Dual-Tone Multi-Frequency).
They are touch tones that are being triggered by cable networks (such as ESPN, Lifetime, CNN, Court TV, etc.) to local cable systems during commercial breaks to run their "local insertion" ads (usually on the half hour and on the hour and last for a minute.) They usually trigger 8 seconds before a local break and again immediately after the local break ends and goes back to network programming. It is a three tone sound because they trigger 3 unique numbers, followed by a "#" in the beginning and a "*" at the end.
So as on a cable network, you would see major ads (Coca-Cola, Tide, etc.) and then for a minute you would see ads from a local car dealership, local stores, etc. That is the purpose of the DTMF tones.
