I’ve seen this a lot recently in manuscripts I edited and in television shows: When two people are talking on cell phones and one person disconnects, the other person is left with a dial tone. This does not happen in real life. If one person hangs up on a cell-to-cell call, the other person is simply left with dead air. But for some reason (perhaps to emphasize a dropped or suddenly disconnected call?), writers go out of their way to mention the dial tone in the ear of the person left holding the phone.
It happened just last week on the show Person of Interest, in which the dial tone was loud and clear when kidnappers hung up on a man whose son they’d just kidnapped. The scene was supposed to be tense but all it did was make me yell at the screen in frustration. Details like this may seem small, but anything that takes your readers out of the moment should be avoided.