Man learns secret sound which every listener hears as the best possible word (short story from mid-90s SciFi collection)

In the mid-90s I recall reading the entire short story in a collection (probably SciFi) while standing in the book store. As a poor college student I didn't buy the book, but the story has stuck with me.

Plot Summary: A man learns a secret sound which the listener hears as whatever word would most benefit the speaker. For example, if you're buying a lottery ticket, tell the cashier that you want the numbers [sound] and you'll win the lottery. Unfortunately for the man, there's a secret society which carefully guards the [sound]...

------------------------------------------------------------ The Full Story: A man orders a "get rich" program from a self-made millionaire, but what arrives isn't quite right: rather than the full books and tapes, it's just a single cassette tape (no label) that's blank. Well, *mostly* blank: it's hard to hear, but there's a sound. Sort of like a voice, but not really. [The book uses an interesting graphic for this sound, and it looks like a bunch of words superimposed on each other.]

He's angry about receiving the wrong product and calls the company to complain. Meanwhile, he calls his stock broker and asks, "Hey, have you ever heard of [sound]?"

The next day the stock broker tells him he invested a bunch of his money in the stock he picked, and it resulted in a huge windfall. Weirdly enough, the broker doesn't tell him it's [sound], but rather some ordinary company name. He didn't heard it as the [sound], but instead heard a regular stock.

Meanwhile, the millionaire himself shows up at the protagonist's house, completely frantic, and wants the cassette back. When asked if listened to the cassette, the protagonist lies and says he didn't.

But he did, and uses the [sound] a few more times to make huge amounts of money: he realizes that it's some magical sound that other people hear as whatever word would best benefit the speaker. At some point, the "higher-ups" in some secret, shadowy organization show up and tell the protagonist never to use it again--they KNOW when he does, and they forbid it.

So he stops.

For a while, at least. He uses it again much later, and then realizes people are coming after him to kill him. So he goes to the airport and says, "Book me a flight to [sound]." Gets on the plane, and when he lands he hops in a taxi: "Drive me to [sound]."

But the taxi driver takes him to agents of the shadowy organization. They tell him that his use of the [sound] almost saved him, but the problem was that the taxi driver was one of their agents and didn't take him to where he asked. "You should've used it more, if you wanted to escape us--should've used it to find a safer method of transport."