Given the context of her statement and the audience's positive reaction to it, it appears that Clinton actually said "we aren't going to raise taxes on the middle class," but either she didn't fully enunciate the ending of the word "aren't" or the word didn't come through clearly on the audio recording (or both). Worst case, she simply misspoke and said "are" when she meant "aren't," because she has not announced any changes to her tax platform or said on any other occasion that she plans to raise taxes on the middle class and not the wealthy.

The "n" sound has been edited out of the Trump ad.

In addition to Clinton's policy position on her website and the crowd's reaction,we also have the pre-released transcript of her remarks, and the linguistics expert's analysis.

Sound has been manipulated to Clinton's disadvantage before. Those of us who watched the convention on CSPAN didn't hear the protests as loudly and clearly as those watching coverage on the MSM. Seems that they were mixing recordings of the protesting sections into the master feed of the speakers provided by the DNC in order to enhance and amplify the protests.

Glad to hear that Snopes agrees with Politifact's assessment of what Clinton actually said.

Actually it doesn't make sense that the crowd would react as though she said 'aren't', yet the 'n' is inaudible on the tape.

this morning, (I watch too much stuff about the Trump campaigns) and it was..I think it was AM Joy,
she is the one that said to them that it was not right....THEY DID HAVE SOMETHING TO DO WITH IT

How did he/they think they would get away with such a amateurish trick?

was embedded in an email from Trump, so everyone on his mailing list got it.

In addition to all the horrible true things about him.

a middle-class tax hike during a campaign.