In chapter seven, Daisy Buchanan openly flirts with Jay Gatsby in front of her husband and Nick Carraway remarks that she has an "indiscreet voice." Nick means that Daisy lacks restraint and is willing to say anything she desires because she is self-assured, unabashed, and confident. However, Gatsby responds to Nick's observation by saying, "Her voice is full of money." Gatsby recognizes that Daisy speaks from a position of privilege, authority, and financial security, which is directly associated with her affluent upbringing and elevated social status. Daisy's words carry an entitled air, which is unrestrained, charming, and conceited. Gatsby does not resent this about Daisy but understands that she feels free to express herself at all times precisely because her wealth and status protect her.

Unlike Gatsby, Daisy hails from an affluent family and has enjoyed living in luxury her entire life. She has never had to work for anything and is portrayed as a materialistic and selfish woman. Daisy's entitled, privileged attitude is reflected in her voice, which "jingles" like the sound of money. Nick understands exactly what Gatsby means by this observation, extending it further by comparing Daisy's voice to that of a "king's daughter" or "golden girl."

Ultimately, Daisy's charming, dignified voice corresponds to her self-centered personality. Her privilege allows her to dismiss others' feelings and avoid the consequences of her actions. Daisy not only carries on an affair with Gatsby and plays with his emotions but also allows him to take the blame for Myrtle's death (which Daisy herself caused). Gatsby's comment that Daisy's voice is "full of money" is his way of recognizing her privileged, entitled attitude—though it doesn't make her less appealing to him.

In answering this question, it's important to bear in mind that Gatsby's observation comes just after Nick's remark that Daisy has an indiscreet voice. Gatsby's remark that Daisy's voice is “full of money” is a clear indication that her penchant for making indiscreet remarks is indissolubly linked to her wealth and high social status.

Because Daisy is rich and privileged, she feels unconstrained in what she says. This attitude is mirrored by her actions, which more often than not show a total disregard for other people. The most obvious example of this, of course, would be Daisy's failing to take responsibility for the death of Myrtle Wilson, even though she was behind the wheel of the car that mowed Myrtle down.

Daisy believes herself a class apart, unconstrained by what she regards as the petty rules and standards that apply to those less privileged than herself. And it is somewhat inevitable that everything about her should in some way reflect this entitled attitude. That includes the sound of her voice, which has a distinct jingle of money about it.

To Nick, this may be a source of “inexhaustible charm,” but most of us are likely to conclude that there's also something dangerous about it, something that reveals a certain contempt for basic moral norms and values.

Daisy's voice conveys her security and privilege. She is not used to ever having to speak discreetly because, for her whole life, everyone has always wanted to hear what the wealthy Miss Daisy Fay or Mrs. Daisy Buchanan had to say. She has been raised with money as a member of society's elite, and she has always been an object of interest and admiration to those around her. Her manners are everything that society says is desirable; her clothing, her hair, her speech, everything about her has been held up by society as the ideal.

Daisy has never learned to be discreet, has probably never learned to consider the consequences of her words or actions on the people around her, has likely never had much to say that would not have been of interest to others. She has nearly every kind of privilege that a person can have in her society—except that she is a woman and not a man—and this sense of security and privilege seems infuse her very voice, just as it shapes her behavior. This is a woman who hits and kills another person with a car and yet seems to feel absolutely no remorse or concern for that person at all. Thus, when Gatsby says she has a voice "full of money," it seems as if Gatsby can hear Daisy's privilege in her voice.

It is Nick who first comments on Daisy's voice and what he says is 'she's got an indiscreet voice'. Money and indiscretion are both present in her voice and are therefore linked. Her indiscretion is a factor of her money. Nick himself is thought to be careful by Jordan, so it is not something he is likely to approve of.

By the end Daisy and Tom and by extension rich people like them are seen by Nick as not just indiscreet but irresponsible, their wealth literally allowing them to get away with murder, to escape any responsibility for Gatsby's death. Nick comments 'They were careless people, Tom and Daisy - they smashed up things and creatures and then retreated back into their money or their vast carelessness'. Here money and carelessness are synonymous and Nick is sickened by the sort of behaviour that wealth allows; Daisy and her voice was an earlier image of this.

In this passage from Chapter 7, Nick is trying to pinpoint what is so elusive about the quality of Daisy's voice.  Gatsby notes that her voice is "full of money," meaning she has the tonal quality of never knowing want, of having always been well provided for, of being elitely educated.  These facts are unconsciously conveyed by the lilt of her voice and the inflections of her vowels and consonants.  Gatsby and Nick, on the other hand, are from a working class backgrounds.   Nick still struggles,  but Gatsby has succeeded monetarily.  Still, he has not the history of wealth that backs Daisy's sense of security.  His speech is practiced and measured rather than effortless and secure. 

Gatsby knows the sounds of old money when he hears it. 

Certainly, I think the interpretation of this line as meaning that Daisy's voice is indiscreet has a great deal of merit. When Gatsby says that her voice is full of money, Nick says,

That was it. I'd never understood before. It was full of money—that was the inexhaustible charm that rose and fell in it, the jingle of it, the cymbals' song of it. . . . High in a white palace the king's daughter, the golden girl. . . .

Daisy's voice seems to be full of qualities associated with having lots of money. She makes no effort to modulate her tone, because she's really never had to be concerned about people not wanting to hear her. She has a certain sense of entitlement because she's been brought up to believe that she is important, and she speaks like it. Further, as someone who's never had to worry about where her next meal is coming from, or how to pay the gas bill, for example, the kinds of concerns she's had have been much less significant than those of the lower classes. She's been relatively untouchable, not subject to the everyday and commonplace cares that most people have, because she's always had money. The "charm" of her voice, the "song of it," seems to convey this.

Before the party leaves Tom's estate and heads into the city, Daisy calls from an upper window to ask if they should bring anything to drink with them, and Gatsby comments to Nick that he cannot say anything in Tom's home. When Nick mentions that Daisy has an indiscreet voice, Gatsby says, "Her voice is full of money" (Fitzgerald, 128). Gatsby is essentially indicating that money and wealth are inherently a part of Daisy's character and a major influence in her life, and this is revealed in her tone of voice. Daisy hails from an affluent family and married Tom Buchanan because of his immense wealth. Her primary goal in life is to maintain her upper-class social status, which is something Gatsby notices in her voice. According to Gatsby, the sound of Daisy's voice reveals her superficial, materialistic personality, and he can tell she is only focused on money. Overall, Gatsby is acknowledging that Daisy's tone of voice is elitist and emphasizes her desire for money and a luxurious life.